Electron beam inspection method and apparatus and semiconductor manufacturing method and its manufacturing line utilizing the same

ABSTRACT

An electron beam inspection method including the steps of irradiating an electron beam to an object to be inspected, detecting at least one of a secondary electron and a reflected electron emanated from the object by the irradiation of the electron beam, and obtaining an image of the object from the detected electron. The method further includes the steps of controlling an electric field in a neighborhood of the object for filtering the at least one of the secondary and reflected electron emanated from the object so as to control the contrast of the image, detecting at least one of the secondary and reflected electron emanated from the object which passes through the electric field in the neighborhood of the object by the irradiation of the electron beam, and conducting inspection or measurement of the object on the basis of a detected signal of the detection in the controlled electric field.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 08/824,413, filedMar. 26, 1997 now U.S. Pat. No. 5,986,263, the subject matter of whichis incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus for obtainingan image or a waveform representing a physical property of an objectsuch as a semiconductor wafer with an electron beam, and comparing theimage or waveform with design information or an image obtainedbehorehand to judge a defect, measure the dimension of a specific place,shape information or the fabrication condition of an object such as asemiconductor wafer, or display an image, and relates to an inspectedwafer and its fabrication line in the case where the wafer is the objectin the apparatus.

A conventional method using an electron beam to judge a defect, measureshape information or the fabrication condition of an object such as asemiconductor wafer, or display an image is described in JP-A-5-258703(U.S. Pat. No. 5,502,306), for example. The conventional method includesthe steps of detecting secondary electrons generated at the time ofexposure with an electron beam under the same condition, conductingscanning with the electron beam, obtaining thereby an image of secondaryelectrons, and judging a defect on the basis of the image.

It is now assumed that an object is formed by predetermined materials Aand B. In the case where a certain acceleration voltage Eb of theelectron beam is used, the secondary electron yield ratio η of thematerial A is largely different from that of the material B. In thiscase, a secondary electron image contrast is obtained, and inspectionbetween the material A and the material B is possible. In the case wherea specific acceleration voltage Ea is used, however, the secondaryelectron yield ratio η of the material A becomes equal to that of thematerial B. In this case, there is little contrast in an obtainedsecondary electron image and the image cannot be observed. In theconventional technique, due regard is not paid to such a charge-upphenomenon for each material to be observed.

SUMMARY OF THE INVENTION

In view of the above described problem, an object of the presentinvention is to provide an electron beam inspection method, andapparatus, for reducing the charge-up phenomenon caused when an objectis exposed to an electron beam, obtaining a high-contrast signalrepresenting a physical property by using secondary electrons orback-scattered electrons obtained from the object, and making itpossible to inspect a minute deffect at high speed and with highreliability.

Another object of the present invention is to provide an electron beaminspection method, and apparatus, for adapting the inspection conditionto the charge-up phenomenon caused when an object is exposed to anelectron beam, conducting inspection or measurement on the basis of animage signal representing a physical property by using secondaryelectrons or back-scattered electrons obtained from the object, andmaking it possible to inspect a minute deffect at high speed and withhigh reliability.

Another object of the present invention is to provide an electron beaminspection method, and apparatus, for making it possible to inspectminute resist patterns and insulator patterns which are apt to becharged, with high reliability.

A further object of the present invention is to provide a semiconductorfabrication method and its fabrication line in which minute patterndefects on a semiconductor substrate such as a semiconductor wafer areinspected to improve the yield.

In order to achieve the above described objects, in accordance with thepresent invention, an electron beam inspection method includes the stepsof controlling an acceleration voltage of an electron beam and anelectric field in neighborhood of an object, exposing the object to theelectron beam with the controlled acceleration voltage, detecting in asensor a physical change generated from the object in response to thecontrolled electric field, and conducting inspection or measurement ofthe object on the basis of a signal representing the detected physicalchange.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam and an electric field in neighborhood of an object,exposing the object to the electron beam with the controlledacceleration voltage, detecting in a sensor a physical change generatedfrom the object in response to the controlled electric field, anddisplaying a signal representing the detected physical change on displaymeans.

In accordance with the present invention, a electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam and an electric field in neighborhood of an objectaccording to a kind of a section structure on a surface of the object,exposing the object to the electron beam with the controlledacceleration voltage, detecting in a sensor a physical change generatedfrom the object in response to the controlled electric field, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam and an electric field in neighborhood of an objectaccording to at least a kind of a material on a surface of the object,exposing the object to the electron beam with the controlledacceleration voltage, detecting in a sensor a physical change generatedfrom the object in response to the controlled electric field, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam and an electric field in neighborhood of an objectaccording to a change of a section structure on a surface of the object,exposing the object to the electron beam with the controlledacceleration voltage, detecting in a sensor a physical change generatedfrom the object in response to the controlled electric field, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam and an electric field in neighborhood of an objectaccording to a kind or a change of a section structure on a surface ofthe object, exposing the object to the electron beam with the controlledacceleration voltage, detecting in a sensor a physical change generatedfrom the object in response to the controlled electric field, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of presetting a proper acceleration voltage ofan electron beam and a proper electric field in neighborhood of anobject so as to correspond to a charge-up phenomenon on a surface of anobject, exposing the object to the electron beam in such a state thatthe acceleration voltage is controlled to become the preset accelerationvoltage, detecting in a sensor a physical change generated from theobject in response to the electric field controlled to become the presetelectric field, and conducting inspection or measurement of the objecton the basis of a signal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of presetting a proper acceleration voltage ofan electron beam and a proper electric field in neighborhood of anobject so as to correspond to a charge-up phenomenon on a surface of anobject according to a kind or a change of a section structure on thesurface of the object, exposing the object to the electron beam in sucha state that the acceleration voltage is controlled to become the presetacceleration voltage, detecting in a sensor a physical change generatedfrom the object in response to the electric field controlled to becomethe preset electric field, and conducting inspection or measurement onthe object on the basis of a signal representing the detected physicalchange.

In accordance with the present invention, the charge-up phenomenon isgrasped as a secondary electron yield efficiency in the electron beaminspection method. Furthermore, in accordance with the presentinvention, the acceleration voltage of the electron beam is in the rangeof 0.3 to 5 kV, in the electron beam inspection method. In accordancewith the present invention, the electric field in the neighborhood ofthe object is 5 kV/mm or less, in the electron beam inspection method.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam on a sample, an electric field on the sample, a beamcurrent, a beam diameter, an image detection rate (which is the clockfrequency for reading image signals and which changes the beam currentdensity), image dimensions (which is changed by changing the scan rateof the electron beam and consequently the beam current density),pre-charge (pre-charge on the sample is controlled by blowing anelectron shower), discharge (discharge on the sample is controlled byblowing an ion shower), or a combination of them, exposing an object tothe electron beam, detecting in a sensor a physical change generatedfrom the object, and conducting inspection or measurement of the objecton the basis of a signal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of controlling an acceleration voltage of anelectron beam on a sample, an electric field on the sample, a beamcurrent, a beam diameter, an image detection rate (which is the clockfrequency for reading image signals and which changes the beam currentdensity), image dimensions (which is changed by changing the scan rateof the electron beam and consequently the beam current density),pre-charge (pre-charge on the sample is controlled by blowing anelectron shower), discharge (discharge on the sample is controlled byblowing an ion shower), or a combination of them so as to correspond toa kind or a change of a section structure on a surface of an object,exposing the object to the electron beam, detecting in a sensor aphysical change generated from the object, and conducting inspection ormeasurement of the object on the basis of a signal representing thedetected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of exposing an object to an electron beam,detecting in a sensor a physical change generated from the object, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change under inspectionconditions such as inspection conditions (including a judgment standardand a measurement standard as well) corresponding to a charge-upphenomenon on a surface of the object.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of exposing an object to an electron beam,detecting in a sensor a physical change generated from the object, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change under inspectionconditions such as inspection conditions (including a judgment standardand a measurement standard as well) corresponding to a charge-upphenomenon on a surface of the object according to a kind or a change ofa section structure on the surface of the object.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of exposing an object to an electron beam,detecting in a sensor a physical change generated from the object, andextracting a structural feature of the object from a signal representingthe detected physical change on the basis of a feature extractionparameter corresponding to a charge-up phenomenon on a surface of theobject.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of exposing an object to an electron beam,detecting in a sensor a physical change generated from the object, andextracting a structural feature of the object from a signal representingthe detected physical change on the basis of a feature extractionparameter corresponding to a charge-up phenomenon on a surface of theobject according to a kind or a change of a section structure on thesurface of the object.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of providing a surface of an object withpre-charge (i.e., blowing an electron shower) or discharge (i.e.,blowing an ion shower), exposing the object to an electron beam,detecting in a sensor a physical change generated from the object, andconducting inspection or measurement of the object on the basis of asignal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of providing a surface of an object withpre-charge (i.e., blowing an electron shower) or discharge (i.e.,blowing an ion shower), exposing the object to an electron beam,detecting in a sensor a physical change generated from the object, andextracting a structural feature on the surface of the object from asignal representing the detected physical change.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, potential control means for controlling an acceleration voltageof the electron beam and an electric field in neighborhood of theobject, a sensor for detecting a physical change generated from theobject in response to the electric field controlled by the potentialcontrol means, upon exposure of the object to the electron beam with theacceleration voltage controlled by the potential control means, andimage processing means for conducting inspection or measurement of theobject on the basis of a signal representing a physical change detectedfrom the sensor. In accordance with the present invention, an electronbeam inspection apparatus includes an electron source, a beam deflectorfor deflecting an electron beam emitted from the electron source, anobjective lens for focusing the electron beam emitted from the electronsource upon an object, potential control means for controlling anacceleration voltage of the electron beam and an electric field inneighborhood of the object, a sensor for detecting a physical changegenerated from the object in response to the electric field controlledby the potential control means, upon exposure of the object to theelectron beam with the acceleration voltage controlled by the potentialcontrol means, and display means for displaying a signal representing aphysical change detected from the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, potential control means for controlling an acceleration voltageof the electron beam and an electric field in neighborhood of the objectaccording to a kind or a change of a section structure on a surface ofthe object, a sensor for detecting a physical change generated from theobject in response to the electric field controlled by the potentialcontrol means, upon exposure of the object to the electron beam with theacceleration voltage controlled by the potential control means, andimage processing means for conducting inspection or measurement of theobject on the basis of a signal representing a physical change detectedfrom the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, potential control means for controlling an acceleration voltageof the electron beam and an electric field in neighborhood of the objectaccording to a kind or a change of at least a material on a surface ofthe object, a sensor for detecting a physical change generated from theobject in response to the electric field controlled by the potentialcontrol means, upon exposure of the object to the electron beam with theacceleration voltage controlled by the potential control means, andimage processing means for conducting inspection or measurement of theobject on the basis of a signal representing a physical change detectedfrom the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, potential control means for controlling an acceleration voltageof the electron beam and an electric field in neighborhood of the objectaccording to a kind or a change of a section structure in an electronbeam irradiation area on the object, a sensor for detecting a physicalchange generated from the object in response to the electric fieldcontrolled by the potential control means, upon exposure of the objectto the electron beam with the acceleration voltage controlled by thepotential control means, and image processing means for conductinginspection or measurement of the object on the basis of a signalrepresenting a physical change detected from the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, potential control means for effecting control so as to attain aproper acceleration voltage of the electron beam and a proper electricfield in neighborhood of the object so as to correspond to a charge-upphenomenon on a surface of the object, a sensor for detecting a physicalchange generated from the object in response to the electric fieldcontrolled by the potential control means, upon exposure of the objectto the electron beam with the acceleration voltage controlled by thepotential control means, and image processing means for conductinginspection or measurement of the object on the basis of a signalrepresenting a physical change detected from the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, potential control means for effecting control so as to attain aproper acceleration voltage of the electron beam and a proper electricfield in neighborhood of the object so as to correspond to a charge-upphenomenon on a surface of the object according to a kind or a change ofa section structure on the surface of the object, a sensor for detectinga physical change generated from the object in response to the electricfield controlled by the potential control means, upon exposure of theobject to the electron beam with the acceleration voltage controlled bythe potential control means, and image processing means for conductinginspection or measurement of the object on the basis of a signalrepresenting a physical change detected from the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, control means for controlling an acceleration voltage of anelectron beam on a sample, an electric field on the sample, a beamcurrent, a beam diameter, an image detection rate, image dimensions,pre-charge, discharge, or a combination of them, a sensor for detectinga physical change generated from the object, upon exposure of the objectto the electron beam, and image processing means for conductinginspection or measurement of the object on the basis of a signalrepresenting a physical change detected from the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, control means for controlling an acceleration voltage of anelectron beam on a sample, an electric field on the sample, a beamcurrent, a beam diameter, an image detection rate, image dimensions,pre-charge, dis-charge, or a combination of them so as to correspond toa kind or a change of a section structure on a surface of the object, asensor for detecting a physical change generated from the object, uponexposure of the object to the electron beam, and image processing meansfor conducting inspection or measurement of the object on the basis of asignal representing a physical change detected from the sensor.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, a sensor for detecting a physical change generated from theobject, upon exposure of the object to the electron beam, inspectioncondition creation means for creating inspection conditionscorresponding to a charge-up phenomenon on a surface of the object,image processing means for conducting inspection or measurement of theobject on the basis of a signal representing a physical change detectedfrom the sensor, under the inspection conditions created by theinspection condition creation means.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, a sensor for detecting a physical change generated from theobject, upon exposure of the object to the electron beam, inspectioncondition creation means for creating inspection conditionscorresponding to a charge-up phenomenon on a surface of the objectaccording to a kind or a change of a section structure on the surface ofthe object, image processing means for conducting inspection ormeasurement of the object on the basis of a signal representing aphysical change detected from the sensor, under the inspectionconditions created by the inspection condition creation means.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, a sensor for detecting a physical change generated from theobject, upon exposure of the object to the electron beam, featureextraction parameter creation means for creating a feature extractionparameter corresponding to a charge-up phenomenon on a surface of theobject, and image processing means for extracting a structural featureof the object from a signal representing the physical change detectedfrom the sensor, on the basis of a feature extraction parameter createdby the feature extraction parameter creation means.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, means for providing a surface of the object with pre-charge ordischarge, a sensor for detecting a physical change generated from theobject, upon exposure of the object to the electron beam, and imageprocessing means for conducting inspection or measurement of the objecton the basis of a signal representing a physical change detected fromthe sensor under inspection conditions.

In accordance with the present invention, an electron beam inspectionapparatus includes an electron source, a beam deflector for deflectingan electron beam emitted from the electron source, an objective lens forfocusing the electron beam emitted from the electron source upon anobject, means for providing a surface of the object with pre-charge ordischarge, a sensor for detecting a physical change generated from theobject, upon exposure of the object to the electron beam, and imageprocessing means for extracting a structural feature of the object froma signal representing the physical change detected from the sensor, onthe basis of a feature extraction parameter.

In accordance with the present invention, a semiconductor fabricationline includes a plurality of processing systems for processingsubstrates, a control system for controlling the plurality of processingsystems, an electron beam inspection system for conducting inspection onthe basis of an image signal, the image signal being obtained byexposing a substrate processed by a predetermined processing system toan electron beam, the processing systems being controlled by the controlsystem on the basis of an inspection result obtained from the electronbeam inspection system.

In accordance with the present invention, a semicondutor fabricationmethod includes the steps of controlling an acceleration voltage of anelectron beam and an electric field in neighborhood of an object,exposing the object to the electron beam with the controlledacceleration voltage, detecting in a sensor a physical change generatedfrom a semiconductor substrate in response to the controlled electricfield, and conducting inspection or measurement of the semiconductorsubstrate on the basis of a signal representing the detected physicalchange and thereby fabricating the semiconductor substrate.

In accordance with the present invention, a semicondutor fabricationmethod includes the steps of controlling an acceleration voltage of anelectron beam on a sample, an electric field on the sample, a beamcurrent, a beam diameter, an image detection rate, image dimensions,pre-charge, discharge, or a combination of them, exposing asemiconductor substrate to the electron beam, detecting in a sensor aphysical change generated from the semiconductor substrate, andconducting inspection or measurement of the semiconductor substrate onthe basis of a signal representing the detected physical change andthereby fabricating the semiconductor substrate.

In accordance with the present invention, a semicondutor fabricationmethod includes the steps of exposing a semiconductor substrate to anelectron beam, detecting in a sensor a physical change generated fromthe semiconductor substrate, and conducting inspection or measurement ofthe semiconductor substrate on the basis of a signal representing thedetected physical change under inspection conditions corresponding to acharge-up phenomenon on a surface of the semiconductor substrate andthereby fabricating the semiconductor substrate.

In accordance with the present invention, a result of the inspection ormeasurement is analyzed and fed back to a predetermined process, in thesemicondutor fabrication method.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of exposing a sample having a pattern formedon a surface thereof to an electron beam, controlling an accelerationvoltage of the electon beam and an electric field in neighborhood of thesample according to the material in an area on the sample exposed to theelectron beam, detecting secondary electrons or back-scattered electronsgenerated from the sample, and thereby inspecting the pattern on thesample.

In accordance with the present invention, the acceleration voltage ofthe electron beam is controlled on the basis of a difference between thesecondary electron yield ratio of the pattern and the secondary electronyield ratio of portions other than the pattern, in the electron beaminspection method. In accordance with the present invention, theelectric field in the neighborhood of the sample surface is controlledon the basis of the secondary electron yield ratio of the pattern, inthe electron beam inspection method.

In accordance with the present invention, an electron beam inspectionmethod includes the steps of exposing a sample having a pattern formedon a surface thereof to an electron beam, controlling an accelerationvoltage of the electron beam and an electric field in neighborhood ofthe sample according to the material in an area on the sample exposed tothe electron beam, counteracting charges stored on the sample surface,detecting secondary electrons or back-scattered electrons generated fromthe sample, and displaying an image of the detected secondary electronsor back-scattered electrons on a screen, and thereby inspecting thepattern on the sample.

As heretofore described, the present invention makes it possible toreduce the charge-up phenomenon caused when an object is exposed to anelectron beam, obtain a high-contrast signal representing a physicalproperty by using secondary electrons or back-scattered electronsobtained from the object, and inspect a minute deffect at high speed andwith high reliability.

Furthermore, the present invention makes it possible to adapt theinspection condition to the charge-up phenomenon caused when an objectis exposed to an electron beam, conduct inspection or measurement of thebasis of an image signal representing a physical property by usingsecondary electrons or back-scattered electrons obtained from theobject, and inspect a minute deffect at high speed and with highreliability.

Furthermore, the present invention makes it possible to inspect minuteresist patterns and insulator patterns which are apt to be charged, withhigh reliability.

Furthermore, the present invention makes it possible to inspect minutepattern defects on a semiconductor substrate such as a semiconductorwafer with high reliability and improve the yield.

Furthermore, the present invention makes it possible to inspect minutepattern defects on a semiconductor substrate such as a semiconductorwafer with high reliability and consequently makes it possible toinspect minute pattern defects on a wafer having minute pattern linewidths in a fabrication line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the relations between acceleration voltage Eand secondary electron yield ratio η for a plurality of materialsaccording to the present invention;

FIGS. 2A and 2B are diagrams showing an example of a detected image inthe case where the secondary electron yield ratios η are made close toeach other for a plurality of materials by making the accelerationvoltage nearly equal to Ea;

FIG. 3 is a schematic sectional view showing how an object having asurface section structure formed by a material A (upper layer pattern)and a material B (lower layer pattern) according to the presentinvention is exposed to an electron beam and the material A (upper layerpattern) is charged up so as to become positive;

FIGS. 4A through 4C are diagrams illustrating defect shrinkage caused inthe detected image when the material A (upper layer pattern) is chargedup so as to become positive as shown in FIG. 3;

FIGS. 5A and 5B are diagrams illustrating shrinkage of the upper layerpattern caused in the detected image when the material A (upper layerpattern) is charged up so as to become positive;

FIGS. 6A through 6E are diagrams showing that the influence of charge-upexerted on the detected image when the material A (upper layer pattern)is charged up so as to become positive appears in relation to thehigh-speed scanning direction of the electron beam and showing masksignals;

FIG. 7 is a schematic sectional view showing how an object having asurface section structure formed by a material A (upper layer pattern)and a material B (lower layer pattern) according to the presentinvention is exposed to an electron beam and how the material A (upperlayer pattern) is charged up so as to become negative;

FIGS. 8A through 8C are diagrams showing a contrast fall appearing inthe detected image as the influence of charge-up when the material A(upper layer pattern) is charged up so as to become negative and showingmask signals;

FIGS. 9A and 9B are diagrams illustrating a change of detected imagecaused according to the number of scans when the material A (upper layerpattern) is charged up so as to become negative;

FIG. 10 is a diagram showing a change of the secondary electron yieldratio η in the case where a positive or negative electric field α isgiven to a certain material according to the present invention;

FIG. 11 is a diagram illustrating an embodiment of setting a properacceleration voltage E and a proper electric field α so as to reduceoccurrence of charge-up in a surface section structure of an objecthaving an upper layer pattern made of the material A and a lower layerpattern made of the material B according to the present invention;

FIG. 12 is a diagram illustrating an embodiment of setting a properacceleration voltage E and a proper electric field α so as to reduceoccurrence of charge-up in a surface section structure of an objecthaving an upper layer pattern made of the material B and a lower layerpattern made of the material A according to the present invention;

FIG. 13 is a diagram showing a first embodiment of a system fordetecting a pattern on an object according to the present invention;

FIGS. 14A through 14C are diagrams illustrating various sequences in asystem for detecting a pattern on an object according to the presentinvention;

FIG. 15 is a schematic configuration diagram showing an embodiment ofhardware configuration of an inspection condition corrector and aninspection condition setter according to the present invetion;

FIG. 16 is a diagram showing a second embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 17 is a diagram illustrating the phenomemon of charge-up occurringon the down stream side of a pattern as the detected image signal in thecase where reciprocating scanning is conducted with an electron beam;

FIG. 18 is a diagram showing an embodiment of a semiconductorfabrication line according to the present invention;

FIG. 19 is a diagram showing a third embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 20 is a diagram showing a fourth embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 21 is a diagram showing a fifth embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 22 is a diagram showing a sixth embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 23 is a diagram showing a seventh embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 24 is a diagram showing an eighth embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 25 is a diagram showing a ninth embodiment of a system fordetecting a pattern on an object according to the present invention;

FIG. 26 is a diagram showing a tenth embodiment of a system fordetecting a pattern on an object according to the present invention; and

FIG. 27 is a diagram showing an eleventh embodiment of a system fordetecting a pattern on an object according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a pattern inspection method for inspecting patterndimensions and defects on an object such as a semiconductor wafer byusing an electron beam and of a fabrication method of a semiconductorwafer according to the present invention will now be described byreferring to drawing.

The case where a semiconductor wafer is used as an object will bedescribed. The same holds true also for other objects such as aphotomask, thin film multilayer substrate, printed circuit board or TFTsubstrate.

By using an electron beam according to the present invention, a patternon an object such as a semiconductor wafer is detected. An embodiment inwhich the pattern of the object is formed by a material A and a materialB as shown in a sectional view of FIG. 3 will first be described. Thisobject forms a solid section structure having a layer made of thematerial A and a layer made of the material B. In the case where anobject thus forming a solid section structure having different materialsis exposed to an electron beam, there is sometimes little contrast at aspecific acceleration voltage. This will now be described by referringto FIG. 1. FIG. 1 shows the relation between the acceleration voltage Eand the secondary electron yield ratio η in the case of the material A1and the material B2. In the case where the acceleration voltage Eb isused, the secondary electron yield ratio of the material A1 is largelydifferent from that of the material B2 as evident from FIG. 1.Therefore, a secondary electron image obtained from the material A1 andthe material B2 has sufficient contrast as shown in FIG. 2A. Inspectionincluding measurement as well (inspection of the dimension or defect) isthus possible. On the contrary, if a specific acceleration voltage Ea isused, then the secondary electron yield ratio of the material A1 isequal to that of the material B2, and there is little contrast in thesecondary electron image obtained from the material A1 and the materialB2. In this case, therefore, a resultant image has little contrast, andinspection including measurement as well (inspection of the dimension ordefect) becomes thus impossible. The specific acceleration voltage Eadiffers depending upon the material. According to the material of theobject, therefore, the suitable acceleration voltage differs.

By using an electron beam according to the present invention, a patternon an object such as a semiconductor wafer is detected. An embodiment inwhich the pattern of the object is formed by a material A3 and amaterial B4 will now be described by referring to FIG. 3, FIGS. 4A, 4Band 4C, FIG. 5, and FIGS. 6A, 6B, 6C, 6D and 6E. As shown in FIG. 3, anobject having a solid section structure and including an upper layermade of the material A3 (such as a circuit pattern which is conductive)and a lower layer made of the material B4 (such as an interlayerinsulator which is a dielectric) is exposed to an electron beam. It isnow assumed that such a condition that the material B4 is charged up soas to be negative is then satisfied. In other words, the secondaryelectron yield ratio η is unity or less (which means that the irradiatedelectron beam is absorbed and consequently the yielded secondaryelectrons are significantly reduced as compared with the irradiationelectron beam). In addition, it is also assumed that such a conditionthat the material A3 is charged up so as to be positive is satisfied. Inother words, the secondary electron yield ratio η is unity or more(which means that secondary electrons nearly equivalent to theirradiation electron beam are yielded). In the case where the degree ofcharge-up is low, a defect 7 of the material A3 appears bright indetection, to say nothing of the material A3 as shown in FIG. 4A. Thematerial B4 appears dark in detection, and a defect 7 of the material A3forced out into the portion which should originally be the material B4also appears bright in detection. In the case where the charge-up isintense, however, there is positive charge-up in the material A3 locatedin the upper layer. Therefore, secondary electrons 6 supplied from thedefect 7 of the material A3 located in the lower layer are drawn towardthe material A3 charged up so as to become positive and are not detectedby a secondary electron detector 16 (11) which will be described laterby referring to FIGS. 13, 14A through 14C, and 17. As shown in FIGS. 4Bor 4C, therefore, the defect appears small in detection or the defectcannot be detected at all. Since information of the inclined portion ofthe material B4 is lost in the same way, the pattern dimension whichshould be detected as shown in FIG. 5A appears small in detection asshown in FIG. 5B.

Furthermore, this phenomenon differs depending upon the speed of ease ofthe charge-up of the object, i.e., the speed of diffusion of electriccharge charged up so as to become positive or negative. If the ease ofcharge-up is fast, the phenomemon is complicated and the scan directiondependency of the electron beam becomes large. Depending upon whetherthe scan direction is X or Y, there occurs a difference in lostinformation. As a result, images as shown in FIGS. 6A and 6B areobtained. When a scan is conducted in the X direction, an influencetends to appear in the neighborhood of the pattern edge in the Xdirection. When a scan is conducted in the Y direction, an influencetends to appear in the neighborhood of the pattern edge in the Ydirection. The diffusion differs depending upon the conductance of thelower layer pattern (material B). If the conductance is large, then thediffusion is extremely fast and the ease of the charge-up is fast.

By using an electron beam according to the present invention, a patternon an object such as a semiconductor wafer is detected. A thirdembodiment in which the pattern of the object is formed by a material A8and a material B9 will now be described by referring to FIGS. 7, 8A, 8Band 8C. As shown in FIG. 7, an object having a solid section structureand including a lower layer made of the material B8 and an upper layermade of the material B4 is exposed to an electron beam 5. It is nowassumed that such a condition that the material B9 is charged up so asto be positive is then satisfied. In other words, the secondary electronyield ratio η is unity or more. In addition, it is also assumed thatsuch a condition that the material A8 is charged up so as to be negativeis satisfied. In other words, the secondary electron yield ratio η isunity or less. In the case where the degree of charge-up is low, thematerial A8 appears dark in detection as shown in FIG. 8A. The materialB9 appears bright in detection. In the case where the charge-up isintense, however, an electric field is formed under the influence ofcharge-up. The electric field formed in the neighborhood is illustrated.An equipotential line 73 of 0 V and a negative equipotential line 72 areformed. When the material A8 is exposed to the electron beam 5 andconsequently secondary electrons 71 are generated, the secondaryelectrons 71 are put back by a repulsive force from the negativeelectric field. Therefore, the secondary electrons 71 cannot arrive at asecondary electron detector 16 (11), and consequently informationconcerning the lower layer is lost. In a portion having a dense patterndensity as shown in FIG. 8B, therefore, a portion which should appearbright in detection appears dark and a suspected pattern occurs on aboundary between different pattern densities.

If charge-up occurs, the secondary electron yield ratio η is changed inboth cases by its own charge-up. As shown in FIGS. 9A and 9B, therefore,an image detected after detection of a plurality of times is changedfrom an image detected at the first time.

In accordance with the present invention, therefore, charge-up is firstprevented from occurring as far as possible at least in a patternlocated in the upper layer (made of the material A) in an object 20. Inother words, the degree of charge-up is lowered. In addition, from thepattern (material A) and a minute spacing of this pattern (material B),a proper contrast value ρ is derived (so as to be high as far aspossible). The condition of inspection including the measurement is madeproper (is corrected) so as to detect images under such a condition.This will now be described in detail. In the object 20, charge-up isprevented from occurring as far as possible at least in the patternlocated in the upper layer (the material A or B) having a characteristicof second electron yield ratio η with respect to an acceleration voltageE for the electron beam used to irradiate the materials A and B as shownin FIG. 1. (The secondary electron yield ratio η from the pattern(material A or B) located in the upper layer is set to a value belongingto a small permitted value range around unity.) In addition, it isattempted to achieve a proper value of contrast ρ. (The secondaryelectron yield ratio η from the material B or A located in the lowerlayer is set to a value belonging to a predetermined range such as arange of 0.7 to 1.2 so as to make the difference from the secondaryelectron yield ratio of the material A or B located in the upper layerthe greatest.) Instead of an image signal significantly influenced bythe charge-up as shown in FIG. 8B, therefore, an image signal reduced ininfluence of the charge-up and having a proper contrast value ρ as shownin FIGS. 4A, 5A or 8A can be detected by the sensor 11. For preventingcharge-up from occurring at least in the pattern located in the upperlayer (material A or B) of the object 20 as far as possible, there canbe used a method of reducing the quantity of the electron beam stored onthe object 20 or a method of exposing the object to an electron showeror an ion shower for counteraction.

The method of reducing the quantity of the electron beam stored on theobject 20 can be implemented by providing proper acceleration voltage(E₀−E₂) for accelerating the electron beam emitted from an electronsource 14 is provided between the object 20 or voltage providing means19 such as a grid passing the electron beam disposed over the object 20and the electron source 14 (which will be described later by referringto FIG. 13 and succeeding drawing) and by providing a proper potentialdifference (E₀−E₁) proportionate to an electric field α on the objectbetween the voltage providing means 19 such as a grid and the object 20.However, the phenomenon of charge-up in the pattern located in the upperlayer changes if the constituent material (material) and sectionstructure of the pattern located in the upper layer are changed.Therefore, it is necessary to set especially the acceleration voltage Eof the electron beam used to irradiate the object and the electric fieldα on the object at proper values with due regard to the constituentmaterial (material) and the section structure of the pattern located inthe upper layer (such as the relation between the constituent material[material] of the upper layer and the constituent material [material] ofthe lower layer, and the shape of the pattern [including the patternwidth and pattern density] and thickness of the pattern). Because thecharge-up phenomenon changes and consequently the second electron yieldratio η changes according to the constituent material (material) and thesection structure of the pattern located in the upper layer (such as theshape of the pattern [including the pattern width and pattern density]and thickness of the pattern and the relation with respect to theconstituent material [material] of the lower layer). In FIG. 1, thesecondary electron yield ratio η is shown as a function of theacceleration voltage E for different materials.

Furthermore, since the charge-up ease phenomenon (diffusion phenomenonof electric charge charged up) occurs in the pattern especially locatedin the upper layer, there occurs a difference in the image signaldetected by the sensor 11 according to whether the scan direction of theelectron beam is the X direction or Y direction as shown in FIGS. 6B and6C. Therefore, it is necessary to set especially the accelerationvoltage E of the electron beam used to irradiate the object and theelectric field α on the object at proper values so as to reduce as faras possible the difference between an image signal detected by thesensor 11 when the scan direction of the electron beam with respect tothe object 20 is the X direction and that when the scan direction of theelectron beam is the Y direction.

Furthermore, in order to inspect the dimension or faults for the patternlocated in the upper layer, it is necessary to set especially theacceleration voltage E of the electron beam used to irradiate the objectand the electric field α on the object at proper values so that thepattern located in the upper layer may be detected with a propercontrast value ρ as the image signal detected by the sensor 11.

By the way, the potential difference (E₀−E₂) represents a potentialdifference between the electron source 14 and the object 20 as describedlater. The potential difference (E₀−E₂) is the acceleration voltage Eshown in FIG. 1. By controlling this potential difference (E₀−E₂), i.e.,the acceleration voltage E, it is possible to change the charge-upphenomenon especially for the pattern located in the upper layer (thematerial A or B), and consequently change the secondary electron yueldratio η. In the case where the electric field α is positive, i.e., thesecondary electrons are decelerated, secondary electrons becomedifficult to be yielded, resulting in a reduced secondary electron yieldratio. On the other hand, in the case where the electric field α isnegative, i.e., the secondary electrons are accelerated, secondaryelectrons become easy to be yielded, resulting in an increased secondaryelectron yield ratio η.

Furthermore, the charge-up phenomenon can be changed and the detectedimage signal can be made proper also by controlling the beam current onthe object, beam diameter, image detection rate (which is the clockfrequency for reading image signals and which changes the beam currentdensity), or the image dimension (which is changed by changing the scanrate of the electron beam and consequently the beam current density).

As heretofore described, according to the material and the sectionstructure of the pattern of the object (such as the shape of the pattern[including the pattern width and pattern density] and thickness of thepattern and the relation with respect to the constituent material[material] of the lower layer), two parameters, for example, (theacceleration voltage E of the electron beam used to irradiate the objectand the electric field α on the object) are controlled according to apredetermined relation. Thereby, the secondary electron yield ratio ηespecially from the pattern located in the upper layer is set in a range(approximately unity) permissible with respect to unity. Thereby, thecharge-up occurring in the pattern located in the upper layer is reducedto become less than a predetermined value so as to hardly occur. Byputting the secondary electron yield ratio η from the material locatedin the lower layer into a predetermined range (such as the range of 0.7to 1.2), the charge-up is reduced as far as possible also for thematerial located in the lower layer. In addition, by making thedifference in secondary electron yield ratio η between the patternlocated in the upper layer and the pattern spacing which is not locatedin the upper layer large as far as possible, the contrast ρ can be madeproper. Under such a condition that the charge-up is not causedespecially for the pattern located in the upper layer, therefore, animage having a sufficient contrast value can be detected by the sensor11 and inspection of the dimension and defects in the pattern having afiner pattern width can be realized with high reliability. In otherwords, with due regard to various factors according to the material andthe section structure of the pattern of the object (such as the shape ofthe pattern [including the pattern width and pattern density] andthickness of the pattern and the relation with respect to theconstituent material [material] of the lower layer), inspection of thedimension and defects in the fine pattern on the semiconductor waferhaving a finer pattern width can be realized with high reliability. Evenin a chip formed on a semiconductor wafer, the material and the sectionstructure of the pattern of the object (such as the shape of the pattern[including the pattern width and pattern density] and thickness of thepattern and the relation with respect to the constituent material[material] of the lower layer) change in some cases. Even in a chipformed on a semiconductor wafer, therefore, it becomes necessary tocontrol the two parameters (the acceleration voltage E of the electronbeam used to irradiate the object and the electric field α on theobject) according to a predetermined relation. If the material and thesection structure of the surface pattern to be inspected as to thedimension and defects change in the object, it is a matter of coursethat it becomes necessary to control the two parameters (theacceleration voltage E of the electron beam used to irradiate the objectand the electric field α on the object) according to a predeterminedrelation. In any case, it will suffice that the condition of twoparameters (the acceleration voltage E of the electron beam used toirradiate the object and the electric field α on the object) suitablefor the material and the section structure of the surface pattern can beset until the time immediately before inspecting the surface pattern ofthe object.

Even if the acceleration voltage E of the electron beam used toirradiate the object and the electric field α on the object are madeproper, it is impossible to almost get rid of the charge-up phenomenonand the charge-up ease phenomenon (diffusion phenomenon of the electriccharge charged up) especially for the pattern located in the upperlayer. In the case where a defect inspection, for example, is to beconducted for the pattern located in the upper layer on the basis of theimage signal detected by the sensor 11, therefore, a parameter forextracting a structural feature of defects and a defect judgmentstandard (inspection standard) for comparison are determined with dueregard to the charge-up phenomenon and the charge-up ease phenomenon(diffusion phenomenon of the electric charge charged up) for the patternlocated in the upper layer. By doing so, false detection based upon thecharge-up phenomenon and the charge-up ease phenomenon for the patternlocated in the upper layer can be eliminated and the inspection of thedimension and defects in a fine pattern on a semiconductor wafer havinga finer pattern width can be realized with high reliability. If thematerial and the section shape of the pattern of the object (includingthe pattern width and pattern density) are changed, the charge-upphenomenon and the charge-up ease phenomenon (diffusion phenomenon ofthe electric charge charged up) for the pattern located in the upperlayer also change. Therefore, the parameter for extracting thestructural feature of defects and the defect judgment standard forcomparison may be chosen according to the material and the section shapeof the pattern of the object (including the pattern width and patterndensity). Alternatively, the charge-up phenomenon and the charge-up easephenomenon (diffusion phenomenon of the electric charge charged up) forthe pattern located in the upper layer may be detected and the parameterfor extracting the structural feature of defects and the defect judgmentstandard for comparison may be chosen according to the detectedcharge-up phenomenon and the charge-up ease phenomenon (diffusionphenomenon of the electric charge charged up) for the pattern located inthe upper layer.

A first embodiment of a system for detecting a pattern on an object suchas a semiconductor wafer by using an electron beam according to thepresent invention will now be described by referring to FIG. 13. Thepresent system includes an electron source 14 having a potential E₂ withrespect to the ground and generating an electron beam, a beam deflector15 for effecting a scan with the electron beam and conducting imaging,an objective lens 18 for focusing the electron beam upon an object 20,and a potential providing device 19. The potential providing device 19is disposed between the objective lens 18 and the object 20 such as asemiconductor wafer. The potential providing device 19 has a potentialE₁ with respect to the grid and provides a grid or the like with apotential. The present system further includes a wafer holder 21. Theobject 20 is mounted on the wafer holder 21. The wafer holder 21 iscapable of holding the object 20 at a potential E₀ with respect to theground, and has an X-Y stage. The present system further includes asensor 11 for detecting a physical change of secondary electronsgenerated by the object 20 and back-scattered electrons, a height sensor13 for detecting the height of the object 20, and a potential controller23 for controlling the potential values E₀, E₁ and E₂ of respectiveportions which in turn determine the acceleration voltage of theelectron beam for the object 20. The present system further includes afocus controller 22 for controlling the objective lens 18 on the basisof the height of the object 20 detected by the height sensor 13 toeffect focus control, an A/D converter 24 for converting a waveform orimage signal representing the physical property of the object detectedby the sensor 11 to a digital signal, and an image processor 25 forconducting image processing on the digital signal obtained from the A/Dconverter 24 and conducting inspection including the dimensionmeasurement of a pattern located on the object. The present systemfurther includes an inspection condition corrector 27. On the basis ofthe digital signal obtained from the A/D converter 24 so as to corresondto a process index and an object index representing the surface sectionstructure of the object 20, the inspection condition corrector 27corrects inspection conditions (such as conditions of the abovedescribed two parameters [the acceleration voltage E of the electronbeam for the object which is given as a potential difference (E₀−E₂),and the electric field α on the object which is given by a nearlyproportionate relation as a potential difference (E₀−E₁)] or thecharge-up phenomenon to the pattern located in the upper layer andcharge-up ease phenomenon [diffusion phenomenon of the electric chargecharged up]). The present system further includes an inspectioncondition setter 28. By specifying a process index and an object indexrepresenting the surface section structure of the object 20, theinspection condition setter 28 stores the inspection conditions (such asconditions of the above described two parameters [the accelerationvoltage E of the electron beam for the object which is given as apotential difference (E₀−E₂), and the electric field α on the objectwhich is given by a nearly proportionate relation as a potentialdifference (E₀−E₁)] or the charge-up phenomenon to the pattern locatedin the upper layer and charge-up ease phenomenon [diffusion phenomenonof the electric charge charged up]) for each group of objects (for everyobjects having the same surface structure). The inspection conditionsetter 28 thus sets inspection conditions. The present system furtherincludes a deflection controller 47 for controlling the beam deflector15, a stage controller 50 for controlling the wafer holder 21, and awhole controller 26 for controlling the whole of them.

As the sequence of this system, three ways as shown in FIGS. 14A, 14Band 14C can be considered.

In a first scheme, the inspection conditions (such as conditions of theabove described two parameters [the acceleration voltage E of theelectron beam for the object which is given as a potential difference(E₀−E₂), and the electric field α on the object which is given by anearly proportionate relation as a potential difference (E₀−E₁)]) areset at the time of inspection as shown in FIG. 14A. At step 31 a, theobject 20 is loaded. At step 32 a, the object 20 is aligned. From therelation of the charge-up phenomenon based on the secondary electronyield ratio η which is in turn extracted on the basis of the waveform orimage signal representing the physical property of the object 20detected by the sensor 11, and the charge-up ease phenomenon based upona signal change detected by a plurality of scans of the electron beam,an operator then judges and the inspection condition corrector 27corrects and stores the inspection conditions at step 33 a. With respectto the corrected inspection conditions stored in the inspectioncondition corrector 27, the inspection condition setter 28 stores andsets desired inspection conditions at step 34 a. At step 35 a, the wholecontroller 26 controls potential values E₀, E₁ and E₂ of respectiveportions by using the potential controller 23 on the basis of thedesired inspection conditions preset in the inspection condition setter28, focuses an electron beam yielded from the electron source 14 uponthe object 20 by using the objective lens 18, causes a scan by using thebeam deflector 15, detects the physical change of the secondaryelectrons and back-scattered electrons generated by the object 20 byusing the sensor 11, and obtains the waveform or image signalrepresenting the detected physical property of the object. On the basisof this signal, an inspection of the dimension or defects is conductedin the image processor 25. At step 36 a, the object 20 is unloaded.

In a second scheme, the inspection conditions (such as the abovedescribed two parameters [the acceleration voltage E of the electronbeam for the object which is given as a potential difference (E₀−E₂),and the electric field α on the object which is given by a nearlyproportionate relation as a potential difference (E₀−E₁)]) are setbefore inspection as shown in FIG. 14B. At step 31 b, objects havingdifferent surface structures are loaded beforehand for each group ofobjects such as each lot (i.e., for every objects having the samesurface structure). At step 32 b, the object is aligned. From therelation of the charge-up phenomenon based on the secondary electronyield ratio η which is extracted on the basis of the waveform or imagesignal representing the physical property of the object 20 detected bythe sensor 11, and the charge-up ease phenomenon based upon a signalchange detected by a plurality of scans of the electron beam, theinspection condition corrector 27 corrects and stores the inspectionconditions at step 33 b. At step 36 b, each object 20 is unloaded. Atstep 31 c, an object 20 to be subsequently inspected is then loaded. Atstep 32 c, the object is aligned. From the corrected inspectionconditions for each object having the same surface structure stored inthe inspection condition corrector 27, the inspection condition setter28 selects, stores and sets desired inspection conditions correspondingto the object to be actually inspected at step 34 c. At step 35 c, thewhole controller 26 controls potential values E₀, E₁ and E₂ ofrespective portions by using the potential controller 23 on the basis ofthe desired inspection conditions preset in the inspection conditionsetter 28, focuses an electron beam yielded from the electron source 14upon the object 20 by using the objective lens 18, causes a scan byusing the beam deflector 15, detects the physical change of thesecondary electrons and back-scattered electrons generated by the object20 by using the sensor 11, and obtains the waveform or image signalrepresenting the detected physical property of the object. On the basisof this signal, an inspection of the dimension or defects is conductedin the image processor 25. At step 36 c, the object 20 is unloaded.

A third scheme is shown in FIG. 14C. On the basis of the relation of thecharge-up phenomenon and the charge-up ease phenomenon based upon thesecondary electron yield ratio η whcih can be theoretically orempirically calculated from the information of the object, theinspection conditions (such as conditions of the above described twoparameters [the acceleration voltage E of the electron beam for theobject which is given as a potential difference (E₀−E₂), and theelectric field α on the object which is given by a nearly proportionaterelation as a potential difference (E₀−E₁)]) are stored and set in theinspection condition setter 28 before inspection at step 37 d. At step31 d, an object 20 to be subsequently inspected is then loaded. At step32 d, the object 20 is aligned. From the inspection conditions storedand set beforehand in the inspection condition setter 28, desiredinspection conditions are stored and set at step 34 d. At step 35 d, thewhole controller 26 controls potential values E₀, E₁ and E₂ ofrespective portions by using the potential controller 23 on the basis ofthe preset desired inspection conditions, focuses an electron beamyielded from the electron source 14 upon the object 20 by using theobjective lens 18, causes a scan by using the beam deflector 15, detectsthe physical change of the secondary electrons and back-scatteredelectrons generated by the object 20 by using the sensor 11, and obtainsthe waveform or image signal representing the detected physical propertyof the object. On the basis of this signal, an inspection of thedimension or defects is conducted in the image processor 25. At step 36d, the object 20 is unloaded. The inspection condition setting into theinspection condition setter 28 at step 37 d may be conducted even afterthe loading so long as it is conducted before the inspection.

Besides the above described two parameters, the beam current on theobject, beam diameter, image detection rate (which is the clockfrequency for reading image signals and which changes the beam currentdensity), or the image dimension (which is changed by changing the scanrate of the electron beam and consequently the beam current density) canbe considered as the inspection conditions.

Correction of the inspection conditions forming components of thesesystems, setting the inspection conditions based on information from theobject, and setting the corrected inspection conditions will now bedescribed. In other words, it suffices that the relations shown in FIGS.1 and 10 are derived beforehand. If in the section structure (such asthe materials A and B) of the object 20 the dependence of the secondaryelectron yield ratio η upon the acceleration voltage (E=E₀−E₂) betweenthe electron source 14 and the object 20 and the potential difference(E₀−E₁) proportionate to the electric field α on the object is known,i.e., these relation tables are created, then a proper contrast value ρ(given by a difference between the secondary electron yield ratio η fromthe upper layer pattern and the secondary electron yield ratio η fromthe lower layer pattern) indicated by a difference in brightness ofimage signal between the upper layer pattern and the lower layer patterncan be chosen so as to prevent the charge-up from occurring with respectto the upper layer pattern within a certain permissible range (i.e., soas to attain a small permissible value range of the secondary electronyield ratio η from the upper layer pattern around unity) and so as tosuppress the charge-up as far as possible for the lower layer pattern aswell (i.e., so as to attain a large permissible value range [such as arange of 0.7 to 1.2] of the secondary electron yield ratio η from thelower layer pattern around unity).

In other words, a proper acceleration voltage Ec is chosen as shown inFIG. 11 so as to make large the difference (contrast ρ) between thesecondary electron yield ratio η (illustrated by solid lines) from theupper layer pattern (material A) and the secondary electron yield ratioη (illustrated by broken lines) from the lower layer pattern (materialB). Thereafter, a potential difference (E₀−E₁) proportionate to theelectric field α on the object is chosen so as to put the secondaryelectron yield ratio η from the upper layer pattern (material A) into asmall permissible value range around unity. If at that time thesecondary electron yield ratio η from the lower layer pattern (materialB) does not come in a large permissible value range around unity, thenproper inspection conditions can be chosen by finely adjusting theacceleration voltage Ec.

Furthermore, a proper acceleration voltage Ec is chosen as shown in FIG.12 so as to make large the difference (contrast ρ) between the secondaryelectron yield ratio η (illustrated by broken lines) from the upperlayer pattern (material B) and the secondary electron yield ratio η(illustrated by solid lines) from the lower layer pattern (material A).Thereafter, a potential difference (E₀−E₁) proportionate to the electricfield α on the object is chosen so as to put the secondary electronyield ratio η from the upper layer pattern (material A) into a smallpermissible value range around unity. If at that time the secondaryelectron yield ratio η from the lower layer pattern (material A) doesnot come in a large permissible value range around unity, then properinspection conditions can be chosen by conducting fine adjustment so asto cause a shift from the acceleration voltage Ec to an accelerationvoltage Ed.

In FIGS. 11 and 12, each of lines of the materials A and B illustratedwith leader lines represents secondary electron yield ratio valuesobtained when the electric field is 0. Each of lines of the materials Aand B which are not illustrated with leader lines represents secondaryelectron yield ratio values obtained when the electric field is changed.In other words, the secondary electron yield ratio of the upper layer (Ain FIG. 11 and B in FIG. 12) is kept in the neighborhood of unity. Forthe purpose of keeping the difference in secondary electron yield ratiobetween the materials A and B at an appropriate value, the electricfield is changed to change the line of secondary electtron yield ratio.

FIG. 15 shows a concrete configuration of an embodiment of theinspection condition corrector 27 (27 a, 27 b) and the inspectioncondition setter 28. Numeral 131 denotes a CPU. Numeral 132 denotes aROM for storing an inspection condition correction processing program.Numeral 133 denotes an image memory for storing digital images obtainedfrom the A/D converter 24. Numeral 134 denotes a RAM for storing variousdata, corrected information of the inspection conditions, and presetinspection conditions. Numeral 135 denotes an input device including akeyboard and a mouse. Numeral 136 denotes a display device such as adisplay. Numeral 137 denotes an external storage device for storinginformation concerning the object such as CAD data. Numeral 138 denotesdesign information including CAD data obtained from the design system.Numerals 139 through 144 denote interface (I/F) circuits. Numeral 145denotes a bus interconnecting the components.

By a command issued by the whole controller 26, respective componentsshown in FIG. 13 are initialized and the stage controller 50 iscontrolled so as to move the object 20 to a predetermined location or alocation specified by the user. According to a command issued by thewhole controller 26, predetermined potential values E₀, E₁ and E₂ areset by the potential controller 23. A focus position determined by thatcondition is set by the focus controller 22. The object 20 is exposed toan electron beam yielded by the electron source 14 via the objectivelens 18 while the electron beam is being deflected by the beam deflector15 based on control of the deflection controller 47. Physical changes ofsecondary electrons and back-scattered electrons generated in the object20 are detected by the sensor 11. A waveform or image signalrepresenting the physical property of the object is thus. detected andconverted to a digital image signal by the A/D converter 24. Theinspection condition corrector 27 stores the digital image signalsupplied from the A/D converter 24 in the image memory 133 and displaysthis stored digital image signal on the display 136. For an area havinga repeated pattern of the displayed digital image signal as shown inFIGS. 2, 4, 6, and 8, the user specifies a pattern located in the upperlayer (material A or B) by using the input device 135. On the basis ofthis specification, the CPU 131 extracts an outline of the abovedescribed pattern (material A or B) from the detected digital imagesignal, stores the shape of the pattern (material A or B) in theexternal storage device (reference) 137, for example, and stores thequantity (such as dose quantity) of the electron beam used to irradiatethe object 20 as well in the RAM 134, for example, by using the inputdevice 135. As for the shape of the pattern (material A or B), it is notnecessary to extract and derive the outline of the above describedpattern (material A or B) from the detected digital image signal, and itis possible to specify an area on the basis of design informationobtained as the CAD data 138. Furthermore, since information especiallyconcerning the uppper layer pattern (such as the shape [including thepattern width and pattern spacing] and thickness) is obtained from theCAD data 138, proper inspection conditions may be chosen by using thisinformation.

In order to position a new area which is located on the object 20 andwhich is not subjected to exposure to the electron beam and charge-up,potential values E₀, E₁ and E₂ are subjected to change control with aconstant pitch, for example, in the potential controller 23 for an areaof each of specified repeated patterns while the stage of the waferholder 21 is being scanned on the basis of the stage controller 50. Anacceleration voltage (E₀−E₂) between the electron source 14 and theobject 20, and a potential difference (E₀−E₁) proportionate to theelectric field α on the object are thus controlled. A waveform or imagesignal representing the physical change of secondary electrons orback-scattered electrons generated from the area of each of specifiedand repeated patterns on the object 20 is detected by the sensor 11,converted to a digital image signal by the A/D converter 24, and storedin the image memory 133. In addition, data of potential values E₀, E₁and E₂ subjected to change control in the potential controller 23 arereceived via the whole controller 26 and stored in the RAM 134, forexample. For the digital image signal stored in the image memory 33, theCPU 131 calculates an image quality such as a secondary electron yieldratio η in a place having an outside shape coinciding with that of apattern (material A or B) stored (registered) in the external storagedevice (reference) 137 and a contrast ρ of the entire image (given by adifference in brightness of digital image signal corresponding to thesecondary electron yield ratio values η of the materials A and B), andstores the calculated image quality in the RAM 134, for example. Out ofimage qualities stored in the RAM 134, for example, the CPU 131 derivespotential values E₀, E₁ and E₂ existing in a small permissible valuerange of the secondary electron yield ratio η around unity (existing insuch a state that charge-up is suppressed to the utmost for the upperlayer pattern) and having the highest image contrast ρ. The CPU 131stores the derived potential values E₀, E₁ and E₂ in the inspectioncondition storage (the RAM 134 or the external storage device 137) asproper inspection conditions. By the way, the secondary electron yieldratio η is defined as a ratio of yielded secondary electrons to theirradiation electron beam. The quantity of the irradiation electron beam(quantity of dose) is stored beforehand in the RAM 134, for example, andis already known. From the strength (brightness) of a digital imagesignal correlative to the yielded secondary electrons detected by thesensor 11 in a place coinciding with the outside shape of a pattern(material A or B), therefore, the CPU 131 can calculate the secondaryelectron yield ratio η as the ratio to the quantity of irradiationelectron beam. In this way, the secondary electron yield ratio η can becalculated as the ratio of the yielded secondary electrons detected bythe sensor 11 to the quantity of the irradiation electron beam.

Furthermore, the contrast ρ in the entire image is given by the ratio ofbrightness intensity averaged over the lower layer pattern to brightnessintensity averaged over the upper layer pattern (in a small permissiblevalue of secondary electron yield ratio η around unity). In other words,the contrast ρ of the entire image is given from the intensity(brightness) of the digital image signal correlative to the yieldedsecondary electrons detected by the sensor 11 in the upper layer pattern(material A) area and its peripheral area (its neighboring area, i.e.,lower layer pattern area) (material B) as shown in FIG. 8B, for example.In this case, the contrast ρ of the entire image is given as the ratioof bright intensity averaged over a plurality of peripheral areas(neighboring areas) to dark intensity (in a small permissible valuerange of secondary electron yield ratio η around unity) averaged over aplurality of pattern (material A) areas. Since the charge-up is affectedby the scan of the electron beam as shown in FIGS. 6B and 6C, it isnecessary to calculate the contrast ρ of the entire image with dueregard to this point. In other words, the contrast ρ of the entire imageis given as the ratio of bright intensity (in a small permissible valuerange of secondary electron yield ratio η around unity) averaged over aportion of a plurality of upper layer pattern areas (material A)affected by the scan to dark intensity averaged over a plurality ofperipheral areas of the upper layer pattern (material A). As a matter ofcourse, it is apparent that the contrast ρ of the portions which areincluded in a plurality of upper layer pattern areas (material A) andwhich are not affected by the scan becomes better. As shown in FIG. 8Bor FIGS. 6B and 6C, therefore, the CPU 131 can calculate the contrast ρof the entire image from the intensity (brightness) of a digital imagesignal correlative to the yielded secondary electrons detected by thesensor 11 in the pattern (material A) area and its peripheral area(neighboring area).

If this concept is expanded so as to be defined as the sum total of theelectron beam quantity which is not stored in the object due toback-scattering of the electron beam used to irradiate the object 20,and irradiation, transmittance, leak, etc. of secondary electrons, thena plurality of sensors may be used instead of a single sensor 11 tomeasure terms other than secondary electrons and the measured value maybe used in the case where the terms other than secondary electronscannot be neglected.

A method for setting optimum inspection conditions will now bedescribed. A two-dimensional image obtained by scanning in the Ydirection at low speed while repetitively scanning with an electron beamin the X direction at high speed is compared with a two-dimensionalimage obtained by scanning in the X direction at low speed whilerepetitively scanning in the Y direction at high speed. The sum σ ofpixel contrast difference values over the entire image for each image,and the image contrast ρ between the upper layer pattern and the lowerlayer pattern (i.e., spacing between upper layer patterns) in either ofthe images are calculated. They are stored as the image quality. (Asmall value of the sum a means that charge-up scarcely occurs in such adirection that a scan is effected with an electron beam at high speed asshown in FIG. 6A [i.e., it means that the secondary electron yield ratioη is approximately unity]. On the contrary, a large value of the sum σmeans that charge-up occurs in such a direction that a scan is effectedwith an electron beam at high speed as shown in FIGS. 6B and 6C.) Amongstored image qualities, potential values E₀, E₁ and E₂ having the sum σof pixel contrast difference values over the entire image which is equalto or less than a fixed permissible value (which means that charge-upscarcely occurs as shown in FIG. 6A) and having the highest value of theimage contrast ρ may be stored as corrected inspection conditions.

An alternative method for setting optimum inspection conditions will nowbe described. The same place is scanned with an electron beam to detectan image a plurality of times. Those images are compared. The sum σ ofpixel contrast difference values over the entire image, and the imagecontrast ρ between the upper layer pattern and the lower layer pattern(i.e., spacing between upper layer patterns) in one of the images arecalculated. They are stored as the image quality. (A small value of thesum σ means that charge-up scarcely occurs even if the same place isscanned with an electron beam [i.e., it means that the secondaryelectron yield ratio η is approximately unity]). Among stored imagequalities, potential values E₀, E₁ and E₂ having the sum σ of pixelcontrast difference values over the entire image which is equal to orless than a fixed permissible value (which means that charge-up scarcelyoccurs) and having the highest value of the image contrast ρ or having aminimum change of an average secondary electron yield ratio η over theentire image may be stored as corrected inspection conditions.

Instead of setting the optimum inspection conditions wholly in anautomatic manner, a calculation result of information required fordetermining the inspection conditions or the detected image itself maybe presented to an operator. From the presented information, theoperator determines the optimum inspection conditions. Even when thismethod is used, a similar effect can be achieved. The evaluationparameters of the image quality and the method for selecting the optimuminspection conditions are not limited to those of the above describedembodiment.

The method for setting the inspection conditions on the basis of theinformation of the object will now be described. Beforehand, relationsof the secondary electron yield ratio η to the acceleration voltage E onthe object of each material and the electric field α on the object asshown in FIGS. 1 and 10 are derived and stored in the external storagedevice 137 or the RAM 134 of the inspection condition corrector 27 shownin FIG. 15. At this time, a waveform or image signal representing aphysical change of secondary electrons and back-scattered electronsgenerated from areas of each of specified and repeated patterns on theobject 20 is detected by the sensor 11, converted to a digital imagesignal by the A/D converter 24, and stored in the image memory 133, andthe secondary electron yield ratio η is calculated from this storeddigital image signal, as described above with reference to theembodiment. Instead of this method, calculation may be effected by usinga theoretical analysis method.

So as to correspond to the process index or object index representingthe surface structure of the object 20, the material (i.e., material ofthe upper layer pattern) located in the upper layer of a sectionstructure including a plurality of materials and forming the object(i.e., object to be inspected), the material (i.e., material of thelower layer pattern) located in the lower layer, the layer thickness andshape of the upper layer pattern, and the scan condition of the electronbeam are specified by using the input device 135. The CPU 131 selectsinspection conditions (such as potential values E₀, E₁ and E₂) suitablefor the surface structure of the specified object 20 from the abovedescribed relation table stored in the external storage device 137 orthe RAM 134, stores the inspection conditions (such as potential valuesE₀, E₁ and E₂) in the RAM 134 and the like in association with theprocess index or object index representing the surface structure of theobject 20. The selection of inspection conditions is conducted bylooking for such conditions that the electron yield ratio η from thematerial located in the upper layer (upper layer pattern) isapproximately unity, the second electron yield ratio η from the materiallocated in the lower layer (lower layer pattern) is in a predeterminedrange of 0.7 to 1.2, for example, and has a difference of some degreewith respect to the electron yield ratio η from the material located inthe upper layer (upper layer pattern), and deriving potential values E₀,E₁ and E₂ associated with such conditions. It is a matter of course thatthe inspection conditions must be chosen with due regard to the layerthickness and shape of the upper layer pattern and the scan condition ofthe electron beam. It is because the charge-up characteristic especiallyfor the upper layer pattern changes.

Inspection condition setting in the inspection condition setter 28 willnow be described. The inspection conditions chosen beforehand in theinspection condition corrector 27 are stored in the RAM 134. In theinspection condition setter 28, therefore, the process index or objectindex representing the surface structure of the object 20 is inputted byusing the input device 135. Thereby, corrected inspection condition(potential values E₀, E₁ and E₂) can be read out from the RAM 134 andset in the potential controller 23 via the whole controller 26.

On the basis of the inspection conditions (potential values E₀, E₁ andE₂) set in the inspection condition setter 28, the potential controller23 controls the potential E₀ for the object 20, the potential E₁ for thevoltage providing device 19 for providing the electric field α on theobject, and the the potential E₂ for the electron source 14. The value(E₀−E₂) represents the potential difference from the electron source 14to the object (sample) 20, and it is the acceleration voltage E shown inFIG. 1. Furthermore, (E₀−E₁) is proportionate to the electric field α onthe object (sample) surface. FIG. 12 shows the secondary electron yieldratio η obtained when the electric field α (proportionate to (E₀−E₁)) ischanged. If the electric field α is positive, i.e., secondary electronsare decelerated, then the secondary electrons become difficult to beyielded, resulting in a decreased secondary electron yield ratio η. Onthe other hand, if the electric field α is negative, i.e., secondaryelectrons are accelerated, then the secondary electrons become easy tobe yielded, resulting in an increased secondary electron yield ratio η.By controlling these two parameters in the potential controller 23according to a predetermined relation, it is possible to attain such astate that the secondary electron yield ratio η is approximately unity(i.e., is in a small permissible value range around unity) for thematerial located in the upper layer (upper layer pattern) and thecharge-up can be thus suppressed to the utmost for the upper layerpattern. Thus the image contrast ρ between the material located in theupper layer (upper layer pattern) and the material which is not locatedin the upper layer (lower layer pattern) can be corrected. Under such acondition that charge-up is not caused for the upper layer pattern,therefore, an image having sufficient contrast can be detected.

Furthermore, owing to them, minute defects and dimensions can beinspected with high reliability in association with the surfacestructure of the object. As a result, it became possible to inspectminute pattern defects and dimensions of a wafer having a finer patternwidth in a fabrication line. Especially by using an electron beam,defects and dimensions in a pattern such as an optically transparentoxide film or resist can be inspected with high reliability.

A second embodiment of a system for detecting a pattern on an objectsuch as a semiconductor wafer by using an electron beam according to thepresent invention will now be described by referring to FIG. 16. Thepresent system (inspection apparatus) includes an electron source 14 forgenerating an electron beam, a beam deflector 15 for effecting a scanwith the electron beam and conducting imaging, an objective lens(electric optics) 18 for focusing the electron beam on a wafer 20 whichis the object, a potential providing device 19 such as a grid disposedbetween the objective lens 18 and the wafer (object) 20, a wafer holder21 for holding the wafer 20 mounted thereon, a stage 46 for scanning andpositioning the wafer holder 21, an ExB (a device provided with anelectric field E and a magnetic field B) 17 for collecting secondaryelectrons generated from the surface of the wafer 20 to a secondaryelectron detector 16, a height sensor 13, a focus controller 22 foradjusting the focus position of the objective lens 18 on the basis ofthe height information of the wafer surface obtained from the heightsensor 13, a deflection controller 47 for controlling the beam deflector15 to conduct scanning with the electron beam, a potential controller 21including a wafer holder potential adjuster 49 for adjusting thepotential E₀ of the wafer holder 21, a grid potential adjuster 48 forcontrolling the potential E₁ of the voltage providing device 19 such asa grid, and an electron source potential adjuster 51 for controlling thevoltage E₂ of the electron source 14, an A/D converter 24 for conductingA/D conversion on a signal supplied from the secondary electron detector16, an image processor 25 including an image memory 52 and an imagecomparator 53 to process the digital image subjected to A/D conversionin the A/D converter 24, an inspection condition corrector 27 a forcorrecting the inspection conditions on the basis of the digital imagesubjected to A/D conversion, an inspection condition setter 28 forsetting and storing inspection conditions corrected and chosen by theinspection condition corrector 27 a, a stage controller 50 forcontrolling the stage 46, a whole controller 26 for controlling thewhole of them, and an inspection vacuum chamber 45 for housing theelectron source 14, the beam deflector 15, the objective lens (electricoptics) 18, the voltage providing device 19 such as the grid, and thewafer 20 which is the object (sample).

The sequence of the present system is shown in FIG. 14B. In this scheme,inspection conditions are preset before inspection. For each of kindshaving changed surface section structures, a sample (wafer) 20 is loaded(step 31 b). (The surface section structure changes from lot to lot andfrom process to process. The surface section structure of the object tobe inspected might be a resist pattern completed by exposuredevelopment, an insulator pattern having through-holes connecting theupper layer wiring and lower layer wiring between wiring layers, or aninsulator pattern, for example.) The object is aligned (step 32 b). Inthe inspection condition corrector 27 a, inspection conditions are thencorrected (step 33 b). Each object is unloaded (step 36 b).

The correction processing of the inspection conditions conducted in theinspection condition corrector 27 a (step 33 b) will now be described. Acommand is issued to the whole controller 26 by the CPU 131. A commandsupplied from the whole controller 26 initializes the components, drivesand moves the stage 46 to a place specified by the user, and sets thefocus position of the objective lens 18 by using the focus controller 22so as to focus on the height of the sample (wafer) 20 detected by theheight sensor 13. The CPU 131 displays predetermined menus stored in theexternal storage device 137 and the RAM 134 on the display device 136.Out of these menus, the user selects a menu closest to the solidstructure (section structure) of the sample surface (such as especiallythe material of the upper layer pattern and the material of the lowerlayer pattern) by specifying it with the input device 135 such as amouse. The CPU 131 sets the potential E₂ of the electron source 14, thepotential E₁ of the voltage providing device 19 such as the grid, andthe potential E₀ of the wafer holder 21 registered in that menurespectively for the electron source potential adjuster 51, the gridpotential adjuster 48, and the wafer holder potential adjuster 48included in the potential controller 23 via the whole controller 26. Byissuing a command via the whole controller 26, the CPU 131 sets thefocus position determined by the inspection conditions by using thefocus controller 22. By issuing a command via the whole controller 26,the CPU 131 exposes the wafer 20 to an electron beam from the electronsource 14 via the objective lens 18. Secondary electrons generated fromthe surface of the sample (wafer) 20 are collected by the ExB 17. Animage is detected by the secondary electron detector 16 and converted toa digital image signal by the A/D converter 24. The CPU 131 stores thedigital image signal obtained from the A/D converter 24 in the imagememory 133 temporarily and displays it on the display device 135. Out ofthis displayed digital image, the user specifies a pattern havingrepetition and located in the upper portion by using the input device135 such as a mouse. By extracting the outline of that pattern, theshape information of the pattern is calculated and stored in the RAM 134or the external storage device 137. In this way, the pattern shapeinformation inclusive of the repetition pitch is information dependingupon the object to be inspected. Therefore, the pattern shapeinformation may be directly obtained from the CAD data 138 and stored inthe RAM 134 or the external storage device 137. By specification withrespect to an image detected from the secondary electron detector 16 onthe basis of the pattern shape information stored in the RAM 134 or theexternal storage device 137, therefore, the secondary electron yieldratio η obtained from an area of the upper layer pattern or an area ofthe lower layer pattern can be calculated.

In other words, by specifying a partial area of a detected imagecoinciding with the pattern shape of the upper layer pattern specifiedbeforehand by some means, an image of the upper layer area and an imageof the lower layer area are discriminated in the image, and the secondelectron yield ratio is specified from the image data.

In response to a command given from the CPU 131, an area on the wafersubjected to exposure to an electron beam is then made a new surfacearea on which charge-up does not occur. For this purpose, the stagecontroller 50 is driven and controlled via the whole controller 26.While the stage 46 having the wafer holder 21 installed thereon is thusbeing scanned, the potential controller 23 is controlled via the wholecontroller 26 so as to change the potential values E₀, E₁ and E₂ with apredetermined pitch. In response to a command given via the wholecontroller 26, focus offset determined by the condition is set in thefocus controller 22. In response to a command given via the wholecontroller 26, the wafer 20 is exposed to an electron beam from theelectron source 14 via the objective lens 18. According to the changesin the potential values E₀, E₁ and E₂, secondary electrons generatedfrom the surface area of the repeated upper layer pattern and lowerlayer pattern on the wafer 20 are collected by the ExB 17. An image isthus detected by the secondary electron detector 16 and converted to adigital image signal by the A/D converter 24. According to the changesin the potential values E0, E1 and E2 obtained by the A/D converter 24,the CPU 131 stores the digital image obtained from the surface area ofthe repeated upper layer pattern and lower layer pattern on the wafer 20in the image memory 133. In the digital image according to the changesin the stored potential values E₀, E₁ and E₂, it is specified whetherthe area is an area of the upper layer pattern or an area of the lowerlayer pattern on the basis of the shape information of the patternstored in the RAM 134 or the external storage device 137. Thereby, thesecondary electron yield ratio η in the area of the upper layer patternand the area of the lower layer pattern according to changes of thepotential values E₀, E₁ and E₂, and the image quality such as thecontrast ρ in the entire image are calculated and stored in the externalstorage device 137 or the like. (The contrast ρ is represented by adifference between the secondary electron yield ratio η in the area ofthe upper layer pattern and the secondary electron yield ratio η in thearea of the lower layer pattern.) As shown in FIGS. 11 and 12, the CPU131 derives the potential values E₀, E₁ and E₂ existing in a smallpermissible value range of the secondary electron yield ratio η from theupper layer pattern around unity (nearly approximated to unity)(existing in such a state that charge-up is suppressed to the utmost forthe upper layer pattern), existing in a large permissible value range ofthe secondary electron yield ratio η from the lower layer pattern aroundunity (existing in such a state that charge-up is suppressed as far aspossible for the lower layer pattern), and yielding a proper imagecontrast value ρ. The CPU 131 stores the derived potential values E₀, E₁and E₂ in the external storage device 137 or the like as inspectionconditions (potential values E₀, E₁ and E₂) in association with a kindof a change of the surface section structure of the object to beinspected (including the process). At the time of image detection, thefocus controller 22 causes follow-up control to a focus positionobtained by adding the focus offset to the output of the height sensor13. Furthermore, on the basis of actually inspected defect information(especially false detection information) obtained from the imagecomparator 53, for example, included in the image processor 25 or theinspection judgment standard (defect judgment standard) in the imagecomparator 53, the CPU 131 calibrates (adjusts) the small permissiblevalue range around unity preset for the secondary electron yield ratio ηobtained from the upper layer pattern and the large permissible valuerange around unity preset for the secondary electron yield ratio ηobtained from the lower layer pattern. Thereby, the CPU 131 amends theinspection conditions (potential values E₀, E₁ and E₂). In theinspection condition setter 28, the inspection conditions (potentialvalues E₀, E₁ and E₂) are thus reset. In this way, false detection canbe prevented in actual inspection conducted in the image processor 25.Because the permissible value for the secondary electron yield ratio ηrelates to the inspection judgment standard (defect judgment standard)in the image comparator 53. As a matter of course, the CPU 131 maydirectly calibrate the inspection conditions (potential values E₀, E₁and E₂) on the basis of history associated with the surface sectionstructure of the object to be inspected concerning the actuallyinspected defect information (especially false detection information)obtained from the image comparator 53, for example, included in theimage processor 25. Furthermore, when calculating the secondary electronyield ratio η obtained from the upper layer pattern, or when setting avalue in a small permissible value range around unity for this secondaryelectron yield ratio η, the CPU 131 can select more proper inspectionconditions by conducting adjustment on the basis of information such asthe shape (including the pattern width and pattern spacing) andthickness of the upper layer pattern obtained from the CAD data 138.

Inspection processing conducted on the object to be actually inspected(wafer) 20 will now be described. Before loading the object to beactually inspected (wafer) 20, a kind of a change of the surface sectionstructure of the object to be actually inspected (including the process)is inputted to the inspection condition setter 28 by using the inputdevice 135. Thereby, inspection conditions (potential values E₀, E₁ andE₂) corresponding to the object to be actually inspected stored in theexternal storage device 137 are chosen, and set and stored in the RAM134. Subsequently, the object to be actually inspected (wafer) 20 isloaded on the basis of a command issued by the whole controller 26 (step31 c). Alignment is conducted (step 32 c). In accordance with inspectionconditions (potential values E₀, E₁ and E₂) corresponding to the kind ofthe object to be actually inspected (variety and process of the wafer)which is set and stored beforehand in the RAM 134 of the inspectioncondition setter 28, the electron source potential adjuster 51, the gridpotential adjuster 48, and the wafer holder potential adjuster 48forming the potential controller 23 are controlled so as to obtain thepotential values E₀, E₁ and E₂ (step 34 c). The focus offset determinedby the conditions is set by the focus controller 22. After setting, thestage 46 is driven and run in the Y direction at a constant speed underthe control of the stage controller 50 on the basis of a command givenfrom the whole controller 26. While the stage 46 is being thus run,scanning is repetitively conducted in the X direction at high speed withthe electron beam supplied from the electron source 14 by using the beamdeflector 15 under the control of the deflection controller 47.Secondary electrons obtained from the surface of the object 20 to beinspected are collected into the secondary electron detector 16 by theExB 17. Two-dimensional secondary electron images are consecutivelydetected by the secondary electron detector 16, and converted totwo-dimensional digital secondary electron image signals by the A/Dconverter 24. The two-dimensional digital secondary electron imagesignals are stored in the image memory 52 included in the imageprocessor 25. Among detected two-dimensional digital secondary electronimage signals and two-dimensional digital secondary electron imagesignals stored in the image memory 52, image signals expected to beoriginally the same patterns such as image signals of each chip arecompared with each other by the image comparator 53. Different portionsare detected as defects. Information concerning defects includingcoordinates of positions where defects have occurred is stored in amemory of the image processor 25 or the whole controller 26 (step 35 c).If all places to be inspected have been inspected, the object 20 to beinspected is unloaded from the wafer holder 21 (step 36 c).

Variants different from the above described correction processing of theinspection conditions in the inspection condition corrector 27 a willnow be described.

In a first variant of the present embodiment, the CPU 131 calculates anaverage secondary electron yield ratio η of a range registered andspecified beforehand in the reference instead of calculating thesecondary electron yield ratio η of the place registered and specifiedbeforehand in the reference. From the secondary electron yield ratio ηin an area of the upper layer pattern and an area of the lower layerpattern according to changes in the potential values E₀, E₁ and E₂, theCPU 131 calculates an average secondary electron yield ratio η of arange registered and specified beforehand in the external storage device(reference) 137 (a range including a plurality of repetitions of an areaof the upper layer pattern and an area of the lower layer pattern). TheCPU 131 selects such inspection conditions (potential values E₀, E₁ andE₂) that this calculated average secondary electron yield ratio η comesin a small value range around unity (i.e., it becomes a value which canbe nearly approximated to unity). Thereby, the contrast ρ falls to somedegree. Since charge-up does not occur in an average manner on thesurface of the object to be inspected, however, stable inspection can beconducted for a long time.

In a second variant of the present embodiment, the CPU 131 calculatesthe average secondary electron yield ratio η of the range registered andspecified beforehand in the reference besides the calculation of thesecondary electron yield ratio η of a place registered and specifiedbeforehand in the reference, and selects such inspection conditions thatthe weighted average of them is close to unity. In other words, the CPU131 calculates the secondary electron yield ratio η obtained from anarea of the upper layer pattern according to changes of the potentialvalues E₀, E₁ and E₂ and the secondary electron yield ratio η over theabove described range, and selects such inspection conditions (potentialvalues E₀, E₁ and E₂) that the weighted average of them is close tounity. Thereby, the charge-up of the upper layer pattern and the averagecharge-up can be optimized, and stable inspection can be conducted for along time.

In a third variant of the present embodiment, the CPU 131 calculates thesecondary electron yield ratio η of a place specified by an operatorinstead of calculating the secondary electron yield ratio η of the placeregistered and specified beforehand in the reference. In other words, anarea on the wafer subjected to exposure to an electron beam is then madea new surface area on which charge-up does not occur, in response to acommand given from the CPU 131. For this purpose, the stage controller50 is driven and controlled via the whole controller 26. While the stage46 having the wafer holder 21 installed thereon is thus being scanned,the potential controller 23 is controlled via the whole controller 26 soas to change the potential values E₀, E₁ and E₂ with a predeterminedpitch. In response to a command given via the whole controller 26, focusoffset determined by the condition is set in the focus controller 22. Inresponse to a command given via the whole controller 26, the wafer 20 isexposed to an electron beam from the electron source 14 via theobjective lens 18. According to the changes in the potential values E₀,E₁ and E₂, secondary electrons generated from the surface area of therepeated upper layer pattern and lower layer pattern on the wafer 20 arecollected by the ExB 17. An image is thus detected by the secondaryelectron detector 16 and converted to a digital image signal by the A/Dconverter 24. According to the changes in the potential values E₀, E₁and E₂ obtained by the A/D converter 24, the CPU 131 stores the digitalimage obtained from the surface area of the repeated upper layer patternand lower layer pattern on the wafer 20 in the image memory 133. Thedigital image according to the changes in the stored potential valuesE₀, E₁ and E₂ is displayed on the screen of the display device 136. Forthe digital image according to the changes in the stored potentialvalues E₀, E₁ and E₂, a place (area) where the secondary electron yieldratio η is to be calculated is specified by using the input device 135.Thereby, the secondary electron yield ratio η and the contrast ρ can becalculated in this specified place (area). As a result, registrationinto the reference is not needed. Even for a pattern which does notnecessarily have repetitions, inspection conditions can be chosen. Whilespecifying the potential values E₀, E₁ and E₂ by using the input device135 and observing the digital image according to changes of thepotential values E₀, E₁ and E₂ displayed on the screen of the displaydevice 136, such inspection conditions (potential values E₀, E₁ and E₂)that charge-up is not seen in the upper layer pattern and propercontrast ρ is obtained can be directly chosen and stored in the externalstorage device 137 so as to be associated with the kind of the object tobe inspected (section structure of the surface) without calculating thesecondary electron yield ratio η and the contrast ρ. In the case wherethe CPU 131 attempts to correct the inspection conditions (potentialvalues E₀, E₁ and E₂) by calculating the secondary electron yield ratioη and the contrast ρ, correction of the inspection conditions can beconfirmed by displaying the corrected digital image on the screen of thedisplay device 136.

In a fourth variant of the present embodiment, the CPU 131 calculates anaverage secondary electron yield ratio η of the entire image or in arange specified by the operator instead of calculating the secondaryelectron yield ratio η of the place registered and specified beforehandin the reference. As a result, registration into the reference is notneeded. Even for a pattern which does not necessarily have repetitions,inspection conditions (potential values E₀, E₁ and E₂) can be chosen,and charge-up does not occur in an average manner. Therefore, stableinspection can be conducted for a long time.

In a fifth variant of the present embodiment, the CPU 131 does notcalculate the secondary electron yield ratio η of the place registeredand specified beforehand in the reference. Instead, the CPU 131 detectsa digital image using secondary electrons in a plurality of scan methods(such as a method of changing the scan direction as shown in FIGS. 6Band 6C or a method of scanning the same place a plurality of times insuccession), calculates the degree of coincidence between them (i.e.,the degree of absence of difference between digital images), and selectsinspection conditions (potential values E₀, E₁ and E₂) having a highdegree of coincidence. In the case where charge-up occurs on the surfaceof the object to be inspected, a change should occur in the charge-upphenomenon by conducting scanning with an electron beam a plurality oftimes during a comparatively short time even if there is a charge-upease phenomenon. In the case where a change is not seen (i.e., thedegree of coincidence is high) between detected digital images,therefore, it is indicated that charge-up does not occur on the surfaceof the object to be inspected. Furthermore, as for the contrast ρ, itcan be calculated from the detected digital image. Owing to this,inspection conditions can be chosen without a registered reference orspecification by the operator. On the basis of a difference (change)between detected digital images, the charge-up phenomenon on the surfaceof the object to be inspected, on the contrary, can be grasped.

In a sixth variant of the present embodiment, the CPU 131 does notcalculate the secondary electron yield ratio η of the place registeredand specified beforehand in the reference. Instead, a pattern which canbe detected as the same digital image signal even if the scan directionis changed by 180 degrees on the object is registered beforehand in thereference. By specifying a position of the pattern, an electron beam 172used to irradiate the pattern 171 is aligned via the whole controller 26as shown in FIG. 17. Thereafter, the scan direction of the electron beamis changed with respect to the pattern 171 by 180 degrees. Reciprocatingscanning is thus conducted with the electron beam 172 as represented by173 and 174. A digital image signal obtained from one of scan lines isinverted by 180 degrees so as to form a mirror image. This inverteddigital image signal is compared with a digital image signal obtainedfrom the other scan line, and the degree of their coincidence iscalculated. Inspection conditions (potential values E₀, E₁ and E₂)having a high degree of coincidence and proper contrast ρ calculated onthe basis of a detected digital image are chosen.

FIG. 17 shows an example of a pattern which should provide the samepattern when inverted by 180 degrees so as to form a mirror image.

With respect to this pattern, an image obtained by scanning in thedirection 173 and an image obtained by scanning in the direction 174 areacquired. One of the two images is inverted so as to form a mirrorimage, and comparison is effected. Originally, this pattern is a patternwhich should provide the same pattern when inverted by 180 degrees so asto form a mirror image. If the degree of pattern coincidence is high,therefore, it can be said that pattern detection is accomplishednormally. Otherwise, it is meant that the pattern detection is notproper.

In the case where charge-up has occurred in the pattern 171, a tail 175appears in the downstream of the scan line in the pattern 171 as thedigital image in each of the reciprocating scan lines 173 and 174. Bycomparing a digital image signal obtained by inverting a digital imageobtained from one of the scan lines by 180 degrees with a digital imagesignal obtained from the other of the scan lines, therefore, the tail175 appears on both sides of the pattern 171 as noncoincidence(difference) in the case where charge-up has occurred in the pattern171. If charge-up does not occur in the pattern 171, then the tail 175does not appear in the downstream of the scan line in the pattern 171 asthe digital image in each of the reciprocating scan lines 173 and 174,resulting in a high degree of coincidence. In other words, inspectionconditions (potential values E₀, E₁ and E₂) which do not cause thecharge-up in the pattern 171 can be chosen. According to this variant,proper inspection conditions can be chosen without information of thesection structure of the object to be inspected. By comparing a digitalimage signal obtained by inverting a digital image obtained from one ofthe scan lines by 180 degrees with a digital image signal obtained fromthe other of the scan lines and detecting the tail 175 appearing asnoncoincidence (difference) on both sides of the pattern 171, thecharge-up phenomenon which has appeared in the pattern 171 can begrasped.

In a seventh variant of the present embodiment, the CPU 131 does notcalculate the secondary electron yield ratio η of the place registeredand specified beforehand in the reference. Instead, a certain area onthe object to be inspected is scanned with an electron beam a pluralityof times to detect respective digital images as shown in FIGS. 9A and9B. For example, a digital image detected in a first scan is comparedwith a digital image in a scan conducted a plurality of scans after, andthe degree of coincidence between them is calculated. Inspectionconditions (potential values E₀, E₁ and E₂) having a high degree ofcoincidence and having proper contrast ρ calculated on the basis of thedetected digital image are chosen. If charge-up occurs in the upperlayer pattern, a difference between a digital image detected in a firstscan is compared with a digital image in a scan conducted a plurality ofscans after, for example, becomes large. If on the contrary charge-updoes not occur in the upper layer pattern, then the difference between adigital image detected in a first scan is compared with a digital imagein a scan conducted a plurality of scans after, for example, is littleand the degree of coincidence becomes high. Therefore, inspectionconditions (potential values E₀, E₁ and E₂) causing no charge-up in theupper layer pattern can be chosen. According to this variant, properinspection conditions can be chosen without information of the surfacesection structure of the object to be inspected. In an eighth variant ofthe present embodiment, inspection conditions are not chosenautomatically. Instead, the CPU 131 presents image quality evaluationparameters, such as the secondary electron yield ratio η of a specifiedplace, the degree of coincidence between digital images detected byusing a plurality of scan methods, and contrast of digital images, tothe operator by displaying them on the display device, for example.Thus, the operator selects inspection conditions. According to thepresent variant, proper inspection conditions can be chosen by using asimple configuration.

In a ninth variant of the present embodiment, inspection conditions arenot chosen automatically. Instead, the CPU 131 presents a digital imagedetected in association with changed potential values E₀, E₁ and E₂ tothe operator by displaying them on the display device 136, for example.Thus, the operator selects proper inspection conditions (potentialvalues E₀, E₁ and E₂) on the basis of the observed digital image.According to the present variant, proper inspection conditions can bechosen without information of the surface section structure of theobject to be inspected and with a simple configuration.

Furthermore, it is apparent that a plurality of variants heretoforedescribed may be applied to select proper inspection conditions(potential values E₀, E₁ and E₂).

As heretofore described, the present embodiment makes it possible toinspect wafers (objects to be inspected) of various varieties andprocesses under proper inspection conditions (potential values E₀, E₁and E₂). In addition, it can be realized to inspect defects anddimensions of patterns on wafers (objects to be inspected) havingvarious surface section structures not only of a specific variety butalso of a plurality of processes. As a result, the present embodimentcan be used as a fabrication pattern inspection system 216 as shown inFIG. 18. It can be realized to conduct on-line inspection on minutedefects and dimensions in a resist pattern or an insulator patternhaving a surface section structure which cannot be optically inspectedin the middle of the flow of the fabrication process. As a matter ofcourse, the inspection can be realized off-line.

FIG. 18 shows the schematic configuration of a fabrication sytem usingthe embodiment of FIG. 16 as the fabrication pattern inspection system216. In the fabrication system, wafers (semiconductor substrates) 212are thrown into a fabrication line 211 and fabrication is conducted byusing a large number of fabrication facilities 1 through n. Numeral 213denotes a quality control network for controlling various fabricationconditions (including fabrication lots) inputted from terminals 2141through 214n installed in association with a large number of fabricationfacilities 1 through n forming the fabrication line, and quality datainspected by a quality inspection system 215, a fabrication patterninspection system 216, and a probe tester 217. The quality controlnetwork 213 is connected to a quality control computer (notillustrated). Controllers installed in the fabrication facilities may bedirectly connected to the quality control network 213.

The quality inspection system 215 is an inspection system for inspectingforeign particles and conducting line width measurements on the wafer212 fabricated as far as a desired fabrication system by taking at leasta lot as the unit. As the quality inspection system 215, an inspectionsystem for conducting optical inspection and an inspection system usingan electron beam according to the present invention can be used. Thequality inspection system 215 may conduct inspection on-line for thewafer 212 fabricated as far as a desired fabrication system by taking atleast a lot as the unit. By applying also an inspection system using anelectron beam according to the present invention to measurement ofdimensions of a resist pattern (having transparency with respect tolight) subjected to exposure development, measurement and inspectionresults having higher precision as compared with the optical system canbe obtained.

By taking at least a lot as the unit for the wafer 212 fabricated as faras a desired fabrication system, the fabrication pattern inspectionsystem 216 inspects a circuit pattern formed on the surface of a waferor an insulator pattern having through-holes formed therin. As thefabrication pattern inspection system 216, an inspection system forconducting optical inspection and an inspection system using an electronbeam according to the present invention can be used. The fabricationpattern inspection system 216 may conduct inspection on-line for thewafer 212 fabricated as far as a desired fabrication system by taking atleast a lot as the unit in the same way as the quality inspection system215. By applying also an inspection system using an electron beamaccording to the present invention to defect inspection of an insulatorpattern having through-holes formed therein, measurement and inspectionresults having higher precision as compared with the optical system canbe obtained.

The probe tester 217 is a device for inspecting all IC chips formed on acompleted wafer for electric characteristics. From the probe tester 217,therefore, defect items are detected for each of chips on the wafer.

The quality control computer analyzes inspection results obtained fromthe quality inspection system 215, the fabrication pattern inspectionsystem 216, and the probe tester 217 via the quality control network213, thereby estimates the cause of the defect, and determines thefabrication process (fabrication system) giving rise to the defectcause. The information is reported to the terminal of the fabricationsystem. Manufacturing conditions are altered and amended so as toprevent the defect from occurring.

A semiconductor is fabricated on a semiconductor substrate (wafer) via afilm forming dry process for forming an insulator film such as aninterlayer insulator film or a guard film and a wiring metal film, anetching dry process for forming an insulator film pattern having acircuit pattern and through-holes, an exposure development process forconducting resist coating and exposure development and forming a resistpattern, a resist removing process, a planarization process forplanarizing the insulator film, and a cleaning process. Therefore, thesemiconductor fabrication line is formed by disposing a large number offabrication systems 1 through n having various processors forimplementing the above described processes and controllers forcontrolling those processors. An electron beam inspection systemaccording to the present invention is disposed between the abovedescribed desired fabrication systems. Patterns on wafers fabricated bya fabrication system are inspected by this inspection system. A resultof pattern inspection is transmitted to the quality control computer viathe quality control network 213. On the basis of this inspection dataand past quality control data, the quality control computer inquiresinto the cause of the defect and reports it to the terminal of thefabrication facility giving rise to the cause of the defect. Uponreceiving the report, the terminal conducts countermeasure controldepending on the defect cause on the fabrication facility. In order toprevent occurrence of the defect, alteration and amendment (includingcleaning) of the fabrication conditions (process processing conditions),i.e., control is effected.

A third embodiment of a system for detecting a pattern on an object suchas a semiconductor wafer by using an electron beam according to thepresent invention will now be described by referring to FIG. 19. Thepresent system (apparatus) includes an electron source 14 for generatingan electron beam, a beam deflector 15 for effecting a scan with theelectron beam and conducting imaging, an objective lens 18 for focusingthe electron beam on a wafer 20 which is the object to be inspected, apotetial providing device 19 such as a grid disposed between theobjective lens 18 and the wafer 20, a wafer holder 21 for holding thewafer 20 mounted thereon, a stage 46 for scanning and positioning thewafer holder 21, an ExB (a device provided with an electric field E anda magnetic field B) 17 for collecting secondary electrons generated fromthe surface of the wafer to a secondary electron detector 16, a heightsensor 13, a focus controller 22 for adjusting the focus position of theobjective lens 18 on the basis of the height information of the wafersurface obtained from the height sensor 13, a deflection controller 47for controlling the beam deflector 15 to conduct scanning with theelectron beam, a potential controller 21 including a wafer holderpotential adjuster 49 for adjusting the potential E₀ of the wafer holder21, a grid potential adjuster 48 for controlling the potential E₁ of thevoltage providing device 19 such as a grid, and an electron sourcepotential adjuster 51 for controlling the voltage E₂ of the electronsource 14, an A/D converter 24 for conducting A/D conversion on a signalsupplied from the secondary electron detector 16, an image processor 25including an image memory 52 and an image comparator 53 to process thedigital image subjected to A/D conversion in the A/D converter 24, aninspection condition corrector 27 b for correcting the inspectionconditions on the basis of the surface section structure of the objectobtained from the design information, an inspection condition setter 28for setting and storing inspection conditions corrected and chosen bythe inspection condition corrector 27 b, a stage controller 50 forcontrolling the stage 46, a whole controller 26 for controlling thewhole of them, and an inspection vacuum chamber 45 for housing theelectron source 14, the beam deflector 15, the objective lens (electricoptics) 18, the voltage providing device 19 such as the grid, and thewafer 20 which is the object (sample). FIG. 19 differs from FIG. 16 inexistence of the inspection condition corrector 27 b.

The sequence of the present system is shown in FIG. 14C. In this scheme,inspection conditions are preset on the basis of a plurality ofmaterials forming the object 20 to be inspected.

The correction of the inspection conditions conducted in the inspectioncondition corrector 27 b will now be described. As shown in FIGS. 1 and10, the CPU 131 theoretically calculates dependence of the secondaryelectron yield ratio η upon the acceleration voltage E on the sample andthe electric field a on the sample for a plurality of materials formingthe surface section structure over the kinds of the object on the basisof experimental values inputted by using the input device 135, andstores the dependence in the external storage device 137. Subsequently,a plurality of materials (a material located in the upper layer and amaterial located in the lower layer) forming the surface sectionstructure according to the kind of the object to be inspected arespecified by using the input device 135. The CPU 131 searches forinspection conditions (potential values E₀, E₁ and E₂) having a valuecontained in a small permissible value range around unity (i.e., havinga value equal to approximately unity) as the secondary electron yieldratio η of the specified material located in the upper layer, having avalue contained in a predetermined permissible value range such as therange of 0.7 to 1.2 as the secondary electron yield ratio η of thematerial located in the lower layer, and having a proper value as thedifference (contrast ρ) from the secondary electron yield ratio η of thematerial located in the upper layer. The CPU 131 stores such inspectionconditions (potential values E₀, E₁ and E₂) in the external storagedevice 137 as proper inspection conditions (step 37 d). As a matter ofcourse, a group of proper inspection conditions according to the kindare stored in the external storage device 137 over kinds of the objectto be inspected.

Actual inspection of wafers will now be described. Before actuallyinspecting a wafer, inspection conditions corresponding to the kind(including the variety and process) of a wafer to be inspected arechosen out of the group of the inspection conditions (potential valuesE₀, E₁ and E₂) stored in the external storage device 137 and stored inthe RAM 134. Subsequently, the wafer to be actually inspected is loadedin response to a command issued by the whole controller 26 (step 31 d).Alignment is conducted (step 32 d). Thereafter, the inspectionconditions stored in the inspection condition setter 28 are read out.Each of the potential values E₀, E₁ and E₂ is thus controlled by thewafer holder potential adjuster 49, the grid potential adjuster 48, andthe electron source potential adjuster 51 forming the potentialcontroller 23. The focus offset determined by the conditions is set bythe focus controller 22 (step 34 d). After this setting, the stage 46 isdriven in the Y direction at a predetermined speed under the control ofthe stage controller 50 in response to a command given from the wholecontroller 26. (As for this scan in the Y direction, scanning using thebeam deflector 15 may be used together therewith.) While the stage 46 isbeing thus driven in the Y direction, scanning is conducted in the Xdirection with the electron beam supplied from the electron source 14 byusing the beam deflector 15 under the control of the deflectioncontroller 47. Consecutive two-dimensional image signals are detectedfrom the second electron detector 16, and converted to two-dimensionaldigital image signals by the A/D converter 24. The two-dimensionaldigital image signals are stored in the image memory 52 included in theimage processor 25. Among detected two-dimensional digital image signalsand two-dimensional digital image signals stored in the image memory 52,image signals expected to be originally the same (such as image signalsof each of repeated chips, blocks, or unit areas (which may include apattern)) are compared with each other by the image comparator 53.Different portions are judged to be defective on the basis of theinspection standard (judgment standard) and recorded in a memoryincluded in the image processor 25 or the whole controller 26 (step 35d). If all places to be inspected on a wafer 20 have been inspected, thewafer is unloaded (step 36 d).

In a first variant of the present embodiment, inspection conditions(potential values E₀, E₁ and E₂) obtained as a result of search usingonly the information of the object to be inspected are not applied asthey are. Instead, calibration is conducted by using the schemedescribed before with reference to the second embodiment (correction ofinspection conditions based upon digital image signals obtained bydetecting secondary electrons generated from the surface of the objectto be inspected) in the neighborhood of inspection conditions (potentialvalues E₀, E₁ and E₂) obtained by searching. Thereby, inspectionconditions suitable for the surface section structure of an actual wafercan be calculated. In other words, the charge-up phenomenon not onlydepends on the material of the pattern in the surface section structurebut also changes according to the shape or thickness of the upper layerpattern. According to the present variant, accurate inspectionconditions can be set in the shortest time.

In the present embodiment as well, working effects similar to those ofthe above described embodiment can be obtained. In other words, wafersof various varieties and processes can be inspected under optimuminspection conditions. The present embodiment can be applied not only toa specific variety but also to wafers obtained in a plurality ofprocesses.

A fourth embodiment of the system for detecting (observing) a pattern onthe object such as a semiconductor wafer by using an electron beamaccording to the present invention will now be described by referring toFIG. 20. FIG. 20 is a schematic configuration diagram showing anembodiment of an observation SEM according to the present invention. Thepresent system (apparatus) includes an electron source 14 for generatingan electron beam, a beam deflector 15 for effecting a scan with theelectron beam and conducting imaging, an objective lens 18 for focusingthe electron beam on an object 20, a potetial providing device 19 suchas a grid disposed between the objective lens 18 and the object, a waferholder 21 for holding the object 20 mounted thereon, a stage 46 forscanning and positioning the object 20, an ExB (a device provided withan electric field E and a magnetic field B) 17 for collecting secondaryelectrons generated from the surface of the object to a secondaryelectron detector 16, a height sensor 13, a focus controller 22 foradjusting the focus position of the objective lens 18 on the basis ofthe height information of the object surface obtained from the heightsensor 13, a deflection controller 47 for controlling the beam deflector15 to conduct scanning with the electron beam, a potential controller 21including a wafer holder potential adjuster 49 for adjusting thepotential E₀ of the wafer holder 21, a grid potential adjuster 48 forcontrolling the potential E₁ of the voltage providing device 19 such asa grid, and an electron source potential adjuster 51 for controlling thevoltage E₂ of the electron source 14, an A/D converter 24 for conductingA/D conversion on a signal supplied from the secondary electron detector16, an image display unit 54 for displaying digital images obtained byA/D conversion conducted in the A/D converter 24 on a monitor 55 such asa display, an inspection condition corrector 27 b for correcting theinspection conditions on the basis of the surface section structure ofthe object obtained from the design information, an inspection conditionsetter 28 for setting and storing inspection conditions corrected andchosen by the inspection condition corrector 27 b, a stage controller 50for controlling the stage 46, a whole controller 26 for controlling thewhole of them, and an inspection vacuum chamber 45 for housing theelectron source 14, the beam deflector 15, the objective lens (electricoptics) 18, the voltage providing device 19 such as the grid, and thewafer 20 which is the object (sample). FIG. 20 differs from FIGS. 16 and18 in that the image display unit 54 and the monitor 55 are providedinstead of the image processor 25. Since the inspection conditioncorrector 27 b also has the monitor (display device) 136 in addition tothe function of the image display unit 54, the monitor (display device)136 can be used instead of the monitor 55.

As shown in FIG. 14C, the sequence of the present system is similar tothat of the third embodiment. However, the inspection at the step 35 dis conducted as hereafter described. In accordance with an order givenby the operator, the stage 46 is driven in the Y direction at apredetermined speed under the control of the stage controller 50 inresponse to a command given from the whole controller 26. (As for thisscan in the Y direction, scanning using the beam deflector 15 may beused together therewith.) While the stage 46 is being thus driven in theY direction, scanning is conducted in the X direction with the electronbeam supplied from the electron source 14 by using the beam deflector 15under the control of the deflection controller 47. Consecutivetwo-dimensional image signals are detected from the second electrondetector 16, and converted to two-dimensional digital image signals bythe A/D converter 24. The two-dimensional digital image signals arestored in the image memory 52 installed in the image display unit 54.The image display unit 54 cuts out a specified image out of imagesignals stored in the image memory, and enlarges and displays the imageon the monitor 55 to present the image to the operator. Therefore, theoperator can observe a specific partial image on the surface of theobject with enlargement. According to the present embodiment, thesurface of the object can be observed under such a condition thatcharge-up is not caused at any time, irrespective of a change of thematerial of the surface of the object.

A fifth embodiment of the system for detecting a pattern on the objectsuch as a semiconductor wafer by using an electron beam according to thepresent invention will now be described by referring to FIG. 21. FIG. 21is a schematic configuration diagram showing an embodiment of an patternlength measuring apparatus for inspecting dimensions of a patternaccording to the present invention. The present system (apparatus)includes an electron source 14 for generating an electron beam, a beamdeflector 15 for effecting a scan with the electron beam and conductingimaging, an objective lens 18 for focusing the electron beam on anobject 20, a potential providing device 19 such as a grid disposedbetween the objective lens and the object, a wafer holder 21 for holdingthe object 20, a stage 46 carrying the wafer holder 21 to scan andposition the object 20, an ExB (a device provided with an electric fieldE and a magnetic field B) 17 for collecting secondary electronsgenerated from the surface of the object to a secondary electrondetector 16, a height sensor 13, a focus controller 22 for adjusting thefocus position of the objective lens 18 on the basis of the heightinformation of the object surface obtained from the height sensor 13, adeflection controller 47 for controlling the beam deflector 15 toconduct scanning with the electron beam, a potential controller 21including a wafer holder potential adjuster 49 for adjusting thepotential E₀ of the wafer holder 21, a grid potential adjuster 48 forcontrolling the potential E₁ of the voltage providing device 19 such asa grid, and an electron source potential adjuster 51 for controlling thevoltage E₂ of the electron source 14, an A/D converter 24 for conductingA/D conversion on a signal supplied from the secondary electron detector16, an image processor 25 including an image memory for storing adigital image obtained by the A/D conversion in the A/D converter 24 andan measurement processor 56 for measuring dimensions of a predeterminedpattern on the basis of the digital image stored in the image memory, aninspection condition corrector 27 a for correcting the inspectionconditions so as to correspond to the surface section structure of theobject on the basis of the digital image obtained from the A/D converter24, an inspection condition setter 28 for setting and storing inspectionconditions corrected and chosen by the inspection condition corrector 27a, a stage controller 50 for controlling the stage 46, a wholecontroller 26 for controlling the whole of them, and an inspectionvacuum chamber 45 for housing the electron source 14, the beam deflector15, the objective lens (electric optics) 18, the voltage providingdevice 19 such as the grid, and the wafer 20 which is the object(sample). FIG. 21 differs from FIGS. 16 and 19 in that dimensions of thepattern on the object to be inspected are measured in the imageprocessor 25. For measuring the dimensions of the pattern in the imageprocessor 25, there are needed data of the deflection value (scan value)of the electron beam supplied from the deflection controller 47 to thebeam deflector 15 and the displacement value (travel value) representingthe value of the travel of the stage effected by the stage controller50. Therefore, data (position information) 221 of the deflection value(scan value) of the electron beam supplied from the deflectioncontroller 47 to the beam deflector 15 and the displacement value(travel value) representing the value of the travel of the stageeffected by the stage controller 50 are inputted to the image processor25.

As shown in FIG. 14B, the sequence of the present system is similar tothat of the second embodiment. At the step 35 c, however, the stage 46is driven in the Y direction at a predetermined speed under the controlof the stage controller 50 in response to a command given from the wholecontroller 26. While the stage 46 is being thus driven in the Ydirection, scanning is repetitively conducted at high speed in the Xdirection with the electron beam supplied from the electron source 14 byusing the beam deflector 15 under the control of the deflectioncontroller 47. Consecutive two-dimensional image signals are detectedfrom the secondary electron detector 16, and converted totwo-dimensional digital image signals by the A/D converter 24. Thetwo-dimensional digital image signals are stored in the image memoryinstalled in the image processor 25. By using the data (positioninformation) 221 of the deflection value (scan value) of the electronbeam supplied from the deflection controller 47 to the beam deflector 15and the displacement value (travel value) representing the value of thetravel of the stage effected by the stage controller 50, dimensions of adesired pattern formed on the surface of the object are measured on thebasis of the image data stored in the above described image memory. Theresults are stored in the memory included in the image processor 25 orthe whole controller 26 and outputted and presented to the operator asoccasion demands.

According to the present embodiment, patterns on wafers of variousvarieties and processes can be measured under proper inspectionconditions. Dimensions of patterns on not only a wafer of a specificvariety but also wafers obtained in a plurality of processes can bemeasured accurately. As a result, the present embodiment can be used asthe quality inspection system shown in FIG. 18. In the midcourse of afabrication process, fine widths of resist patterns and insulatorpatterns which cannot be optically measured can be accurately measured.As a result, quality inspection can be implemented.

Sixth through tenth embodiments of the system for detecting a pattern onthe object such as a semiconductor wafer by using an electron beamaccording to the present invention will now be described by referring toFIGS. 22 through 27. FIG. 22 is a diagram showing a characteristicportion of the sixth embodiment of the system for detecting a pattern onthe object such as a semiconductor wafer by using an electron beamaccording to the present invention. It is now assumed that in the sixthembodiment charge-up has occurred on the surface of the object 20 to beinspected. For the charge-up phenomenon appearing in the digital imagesignal obtained by converting an image signal using secondary electrons,for example, representing the physical property of the object detectedby the sensor 11 (16) as shown in FIGS. 4 through 6, FIG. 8, and FIG.17, the inspection standard (judgment standard) is changed in the imageprocessor 25. In this way, the influence of this charge-up is mitigated,and inspection can be conducted accurately.

Operation conducted in the inspection condition corrector 27 a in theembodiment shown in FIG. 22 will now be described. On the basis of thedigital image signal representing the physical property of the objectand using secondary electrons, for example, detected by the sensor 11(16) according to the high-speed scan direction with the electron beamand converted by the A/D converter 24, the CPU 131 extracts a changearea of the digital image signal due to charge-up (a change area due tocharge-up) as shown in FIGS. 6B or 6C and FIG. 8B, for example, so as tocorrespond to the high-speed scan direction with the electron beam, foreach of kinds differing in surface section structure of object. Asoccasion demands, the CPU 131 conducts charge-up judgment by derivingaverage brightness in the above described change area. For each kind ofthe object to be inspected, the result is stored in the external storagedevice 137. The extraction of the change area of the digital imagesignal due to occurrence of charge-up can be implemented by, forexample, using two threshold values eliminating the brightness of theupper layer pattern area and eliminating the brightness of the lowerlayer pattern area. Because the brightness of the change area due to thecharge-up lies between the brightness of the upper layer pattern areaand the brightness of the lower layer pattern area. In the inspectioncondition corrector 27 a, therefore, two-dimensional mask data (masksignal) indicating the change area due to charge-up for each of repeatedchips, blocks or unit areas (as shown in FIGS. 6D, 6E and 8C, forexample) are formed in the external storage device 137 for each of kindsof the object so as to be associated with the scan direction ofhigh-speed scan using the electron beam. However, it is desirable toconduct processing for expanding only the change area on thetwo-dimensional mask data (mask signal) representing the change areagenerated by charge-up and store it in the external storage device 137as mask data (mask signal) 222. Furthermore, in repeated chips, blocksor unit areas on the objects of the same kind, there are in some casessurface section structures of a plurality of kinds having differentcharge-up phenomena. Therefore, it is necessary to preparetwo-dimensional mask data so as to accommodate them.

Alternatively, the inspection standard (judgment standard) in the changearea due to charge-up may be determined on the basis of the averagebrightness in the above described change area derived by the CPU 131.Furthermore, the inspection standard (judgment standard) in areas otherthan the above described change area may be determined on the basis ofthe image contrast ρ between the upper layer pattern area and the lowerlayer pattern area.

Actual inspection of the object to be inspected (wafer) will now bedescribed. First of all, the inspection condition setter 28 reads out amask signal corresponding to the kind of the object specified at thetime of actual inspection from the external storage device 137, and setsand stores the mask signal in the RAM 134. Subsequently, the stage 46 isdriven in the Y direction at a predetermined speed under the control ofthe stage controller 50 in response to a command given from the wholecontroller 26. While the stage 46 is being thus driven in the Ydirection, scanning is conducted in the X direction with the electronbeam supplied from the electron source 14 by using the beam deflector 15under the control of the deflection controller 47. Consecutivetwo-dimensional image signals are detected from the sensor 11 (thesecond electron detector 16), and converted to two-dimensional digitalimage signals by the A/D converter 24. The two-dimensional digital imagesignals are stored in the image memory 52 included in the imageprocessor 25. Among detected two-dimensional digital image signals andtwo-dimensional digital image signals stored in the image memory 52,image signals expected to be originally the same (such as image signalsof each of repeated chips, blocks, or unit areas) are compared with eachother by the image comparator 53. At this time, mask data 222 stored inthe RAM 134 are read out. On the basis of data (position information)221 of deflection value (scan value) of the electron beam supplied fromthe deflection controller 47 to the beam deflector 15 and displacementvalue (travel value) representing the value of travel of the stageeffected by the stage controller 50, the mask data 222 read out isaligned with the two-dimensional digital image signal to be compared. Onthe basis of the mask data 222, the inspection standard (judgmentstandard) is made different in the change area from other areas. Aportion where the image signals differ from each other is judged to bedefective and is recorded in the memory in the image processor 25 or thewhole controller 26. In other words, when image signals expected to beoriginally the same (such as image signals of each of repeated chips,blocks, or unit areas) are compared with each other by the imagecomparator 53, the inspection standard (judgment standard) is madedifferent in the change area from other areas (for example, thesensitivity is lowered in the change area due to charge-up) on the basisof the mask data 222. As a result, false detection can be prevented evenif a change is caused in the detected digital image signal by charge-up.

As shown in FIG. 6, the change area due to charge-up changes mainly inrelation to the high-speed scan direction with the electron beam.Therefore, the object 20 to be inspected is rotated by 90 or 180 degreesby rotating the wafer holder 21 by 90 or 180 degrees, for example. Thescan direction with the electron beam is thus changed. Consecutivetwo-dimensional image signals are thus detected again from the sensor 11(secondary electron detector 16), converted to two-dimensional digitalimage signals by the A/D converter 24, and inspected in the imageprocessor 25. By doing so, all areas can be inspected with the sameinspection standard (judgment standard).

FIG. 23 is a diagram showing a seventh embodiment of a system fordetecting a pattern on the object such as a semiconductor wafer by usingan electron beam according to the present invention. In the seventhembodiment shown in FIG. 24, the object 20 (28) is loaded. In responseto a command issued by the whole controller 26, the stage 46 is alignedunder the control of the stage controller 50. Thereafter, a certainchip, block, or unit area (which may include a pattern) is scanned oncewith the electron beam. Consecutive first two-dimensional image signalsare detected from the sensor 11 (secondary electron detector 16),converted to first two-dimensional digital image signals by the A/Dconverter 24, and stored in an image memory 232 included in theinspection condition corrector 27 c and the image memory 52 included inthe image processor 25. Subsequently, the same chip, block, or unit area(which may include a pattern) is scanned with the electron beam aplurality of times. (The high-speed scan direction may be changed.)Consecutive second two-dimensional image signals are detected from thesensor 11 (secondary electron detector 16), and converted to secondtwo-dimensional digital image signals by the A/D converter 24. In acharge-up decision unit 233 formed by a CPU and included in theinspection condition corrector 27 c, difference values between the firsttwo-dimensional digital image signals stored in the image memory 232(133) and the second two-dimensional digital image signals arecalculated. Two-dimensional mask data (mask signal) representing thechange area due to charge-up (as shown in FIGS. 6D, 6E and 8C, forexample) are formed and stored in a memory 234. However, it is desirableto conduct processing of expanding only the change area on thetwo-dimensional mask data (mask signal) representing the change area dueto charge-up and store the result in the memory 234 as mask data (masksignal) 235. The inspection standard (judgment standard) in the changearea due to charge-up may be determined on the basis of averagebrightness in the change area derived by the charge-up decision unit233. Furthermore, the inspection standard (judgment standard) in areasother than the above described change area may be determined on thebasis of the image contrast ρ between the upper layer pattern area andthe lower layer pattern area. Until the mask data 235 are thus createdin the inspection condition corrector 27 c, inspection is not executedin the image comparator 53.

Actual inspection of the object to be inspected (wafer) becomes similarto that of the embodiment shown in FIG. 22. In response to a commandissued by the whole controller 26, the stage 46 is driven in the Ydirection at a predetermined speed under the control of the stagecontroller 50. While the stage 46 is being thus driven in the Ydirection, scanning is conducted in the X direction with the electronbeam supplied from the electron source 14 by using the beam deflector 15under the control of the deflection controller 47. Consecutivetwo-dimensional image signals having repetitions of a chip, block, or aunit area are detected from the sensor 11 (the second electron detector16), and converted to two-dimensional digital image signals by the A/Dconverter 24. Among detected two-dimensional digital image signals andthe first two-dimensional digital image signals stored in the imagememory 52, image signals expected to be originally the same (such asimage signals of each of repeated chips, blocks, or unit areas) arecompared with each other. At this time, mask data 235 stored in thememory 234 are read out. On the basis of data (position information) 221of deflection value (scan value) of the electron beam supplied from thedeflection controller 47 to the beam deflector 15 and displacement value(travel value) representing the value of the travel of the stageeffected by the stage controller 50, the mask data 235 read out isaligned with the first two-dimensional digital image signal to becompared. On the basis of the mask data 235, the inspection standard(judgment standard) is made different in the change area from otherareas. A portion where the image signals differ from each other isjudged to be defective and is recorded in the memory in the imageprocessor 25 or the whole controller 26. In other words, when imagesignals expected to be originally the same (such as image signals ofeach of repeated chips, blocks, or unit areas) are compared with eachother, the inspection standard (judgment standard) is made different inthe change area from other areas (for example, the sensitivity islowered in the change area due to charge-up) on the basis of the maskdata 235. As a result, false detection can be prevented even if a changeis caused in the detected digital image signal by charge-up.

As shown in FIG. 6 and FIG. 17, the change area due to charge-up changesmainly in relation to the high-speed scan direction with the electronbeam. Therefore, the object 20 to be inspected is rotated by 90 or 180degrees by rotating the wafer holder 21 by 90 or 180 degrees, forexample. The scan direction with the electron beam is thus changed.Consecutive two-dimensional image signals are thus detected again fromthe sensor 11 (secondary electron detector 16), converted totwo-dimensional digital image signals by the A/D converter 24, andinspected in the image processor 25. By doing so, all areas can beinspected with the same inspection standard (judgment standard).

FIG. 24 is a diagram showing an eighth embodiment of a system fordetecting a pattern on the object such as a semiconductor wafer by usingan electron beam according to the present invention. In the eighthembodiment of FIG. 24, the same line is scanned on the surface of theobject with an electron beam. While a reciprocating scan is beingconducted or a scan is being conducted twice to effect a two-dimensionalscan, consecutive two-dimensional image signals having repeated chips,blocks or unit areas are detected from the sensor 11 (secondary electrondetector 16) and converted to two-dimensional digital image signals bythe A/D converter 24. Numeral 241 denotes a memory for storing a digitalimage signal of one preceding scan line obtained from the A/D converter24 as a result of the reciprocating scan or scanning twice. The memory241 is formed by a shift register. Numeral 242 denotes an image additioncircuit for adding together the digital image signal of one precedingscan line obtained from the memory 241 and the digital image signal ofone succeeding scan line obtained from the A/D converter 24. In the caseof reciprocating scan, it is necessary in the image addition circuit 242to read out the digital image signal of one preceding scan line from thememory 241 with inversion of 180 degrees. Numeral 243 denotes a gatecircuit, which is closed during the preceding scan included in thereciprocating scan or two scans.

In the embodiment shown in FIG. 24, the object 20 (28) to be inspectedis loaded. In response to a command issued by the whole controller 26,the stage 46 is aligned under the control of the stage controller 50.Thereafter, a certain chip, block, or unit area (which may include apattern) is scanned with the electron beam in a two-dimensional way byeffecting a reciprocating scan or effecting two scans. Consecutivetwo-dimensional image signals for the reciprocating scan or two scansare detected from the sensor 11 (secondary electron detector 16), andconverted to two-dimensional digital image signals for the reciprocatingscan or two scans by the A/D converter 24. For the chip, block, or unitarea, a difference between the two-dimensional digital image signalbased upon a preceding scan line in the reciprocating scan or two scansobtained from the memory 241 and the two-dimensional digital imagesignal based upon a succeeding scan line in the reciprocating scan ortwo scans obtained from the A/D converter 24 is calculated in acharge-up decision unit 233 formed by a CPU and other components andincluded in an inspection condition corrector 27 d. Two-dimensional maskdata (mask signals) representing the change area due to charge-up (asshown in FIGS. 6D, 6E and 8C) are thus formed and stored in a memory234. However, it is desirable to conduct processing of expanding onlythe change area on the two-dimensional mask data (mask signals)representing the change area due to charge-up and store the result inthe memory 234 as mask data (mask signal) 235.

Actual inspection of the object (wafer) to be inspected is conducted inthe same way as the embodiments shown in FIGS. 22 and 23. Since thetwo-dimensional digital image signal to be inspected is obtained byaddition conducted in the addition circuit 242, the signal-to-noiseratio is improved and inspection with high reliability can beimplemented. As the scan using the electron beam becomes complicated,however, it becomes necessary to align the digital image signal obtainedby the reciprocal scan or two scans more accurately.

FIG. 25 is a diagram showing a ninth embodiment of a system fordetecting a pattern on the object such as a semiconductor wafer by usingan electron beam according to the present invention. In the ninthembodiment shown in FIG. 26, image signals expected to be originally thesame (such as image signals of each of repeated chips, blocks, or unitareas) are compared with each other and defect candidates are detectedas noncoincidence in an image comparator 254. Two compared imagesincluding defect candidates are cut out respectively by cutout circuits255 and 256 and stored temporarily respectively in image memories 257and 258. In a detail analyzer 259, the inspection standard (judgmentstandard) is altered by using the two-dimensional mask data (masksignal) representing the change area due to charge-up. In this way,attention is paid to charge-up and it is made possible to inspect realminute defects.

A delay circuit 251 functions to delay the digital image signals by avalue corresponding to repeated chips, blocks or unit areas. The delaycircuit 251 is formed by a shift register, for example. Each of theimage memories 252 and 253 functions to store digital images of an areaformed by a plurality of scan lines. An image comparator 254 functionsto compare the image signals respectively stored in the image memories252 and 253 and expected to be originally the same and extract defectcandidates as noncoincidence. The cutout circuits 255 and 256 functionto cut out digital image signals including defect candidates extractedby the image comparator 254 from the image memories 252 and 253 andstore them in the image memories 257 and 258, respectively. The detailanalyzer 259 conducts detailed analysis of digital images includingdefect candidates cut out respectively in the image memories 257 and 258by altering the inspection standard (judgment standard) on the basis ofthe two-dimensional mask data (mask signal) representing the change areadue to charge-up obtained from the inspection condition setter 28. Thusthe detail analyzer can inspect real minute defects. In the case whereit takes a long time for detail analysis, it is possible in the presentembodiment to inspect real minute defects without synchronism with theoccurrence of images detected from the sensor 11 (secondary electrondetector 16) and without being significantly affected by charge-up.Especially for detecting real minute defects, it is necessary to aligndigital images with each other more accurately than the minute defectsize to be detected. For that purpose, position deviation detection alsobecomes necessary. Furthermore, it is necessary to extract a pluralityof features by using a plurality of parameters and effect judgment onthe basis of inspection standard (judgment standard) prepared so as toconform to the extracted feature. Thus, it takes a long time to conductdetail analysis.

FIG. 26 is a diagram showing a tenth embodiment of a system fordetecting a pattern on the object such as a semiconductor wafer by usingan electron beam according to the present invention. It is now assumedthat a shrunk pattern is detected in the detected image due to charge-upas shown in FIG. 5B. In the case where image signals for each ofrepeated chips, blocks, or unit areas are compared with each other,patterns are shrunk in the same way in the compared image signals andconsequently defects can be detected as noncoincidence. In the casewhere the structural features of pattern dimensions (such as a patternwidth or thickness) are extracted, however, it is necessary to alterparameters for extracting structural features according to a changeincurred in the detected image by charge-up.

The tenth embodiment in this case will now be described by referring toFIG. 26. A reference target (reference sample) having the same surfacesection structure (especially the same material) as the object to beinspected and having dimensions measured by using another method andalready known is placed on the wafer holder 21. The reference target isscanned with an electron beam in a two-dimensional way. Two-dimensionalimage signals are detected from the sensor 11 (secondary electrondetector 16) and converted to two-dimensional digital image signals bythe A/D converter 24. In the inspection condition corrector 27 a, afeature value such as a dimension of the reference target is calculatedon the basis of the converted two-dimensional digital image signals, anda difference between it and a feature value such as a dimension of thereference target already known is derived. As shown in FIG. 5B, forexample, a change rate of the feature value such as the shrinkageratioof the pattern due to charge-up is calculated and stored in theexternal storage device 137. In the case where there are a large numberof surface section structures, it is possible to reduce the number ofprepared reference targets by grouping and conduct interpolation orcompensation in each group by using design information of the surfacesection structure of the object to be inspected.

In the inspection condition setter 28, a change rate 264 of the featurevalue according to the surface section structure of the object to beinspected is read out and set. As for parameter setter 261 included inthe image processor 25, various parameters for structural featureextraction such as pattern dimensions (such as the pattern width andpattern thichness) according to the kind of the surface sectionstructure of the object to be inspected are inputted thereto and storedtherein. By specifying the kind of the object to be inspected, aparameter suitable for the desired kind of the object to be inspected isread out of various parameters for structural feature extraction such aspattern dimensions set and stored in the parameter setter 261. Acompensator 262 executes compensation on the parameter thus read outaccording to the change rate 264 of the feature value.

In an image detected under a specific condition, the feature value to bemeasured changes. This change rate is read into the parameter setter261. The change rate is applied in the compensator 262 to the measuredfeature value. The measured feature value is thus compensated to becomea real value.

On the basis of the compensated parameter, a structural feature valueextractor 263 extracts the feature value (such as pattern dimensions) ofthe surface section structure from the two-dimensional digital imagesignal of the object 20 (28) obtained from the A/D converter 24. Inother words, the structural feature value extractor 263 extracts thefeature value of the surface section structure of the object on thebasis of the data (position information) 221 of deflection value (scanvalue) of the electron beam supplied from the deflection controller 47to the beam deflector 15 and displacement value (travel value)representing the value of the travel of the stage effected by the stagecontroller 50. In the structural feature value extractor 263, theparameter for extracting the structural feature value is thuscompensated. As a result, the structural feature value on the surface ofthe object to be inspected can be extracted with due regard to thecharge-up phenomenon occurring on the surface of the object 20 (28) tobe inspected.

By comparing the structural feature value (such as pattern dimensions)extracted in the structural feature value extractor 263 with theinspection standard (judgment standard), inspection can be executed.

An eleventh embodiment of a system for detecting a pattern on an objectsuch as a semiconductor wafer by using an electron beam according to thepresent invention will now be described by referring to FIG. 27. Numeral14 denotes an electron source, and numeral 15 denotes a beam deflector.Numeral 16 denotes a secondary electron detector. Numeral 21′ denotes awafer chuck for supporting an object 20 to be inspected such as a waferwith needles connected to the ground. Therefore, electric charges of theelectrified object 20 to be inspected are released through the needles272. The charge-up ease phenomenon thus occurs. Numeral 46 denotes anX-Y stage. Numeral 271 denotes a line width measuring device forposition monitoring which detects the position of the X-Y stage 46 andposition coordinates on the object 20 to be inspected. Numeral 273denotes an electron shower generator. The electron shower generator 273blows an electron shower against the object 20 to such a degree thatsecondary electrons are not generated. The electron shower generator 273thus counteracts positive charge-up and prevents occurrence ofcharge-up. Numeral 274 denotes an ion shower generator. The ion showergenerator 274 blows an ion shower against the object 20 to such a degreethat secondary electrons are not generated. The ion shower generator 274thus counteracts negative charge-up and prevents occurrence ofcharge-up. Numeral 275 denotes a mesh electrode provided with negativepotential. When a desired place of the object 20 to be inspected isexposed to the focused electron beam 5, the mesh electrode 275 functionsto cause the secondary electron detector 16 to detect properly secondaryelectrons generated from the surface of the object 20 to be inspected.Numeral 24′ denotes an image input unit for inputting two-dimensionalsecondary electron image signals detected by the secondary electrondetector 16. The image input unit 24′ includes an A/D converter 24.Numeral 25 denotes an image processor including the image memory 52 andthe image comparator 53. On the basis of the two-dimensional secondaryelectron image signals inputted to the image input device 24′ and theposition coordinates on the object 20 obtained from the length measuringdevice 271 for position monitoring, the image processor 25 inspects theupper layer pattern and the like. Numeral 26 denotes a control computer(whole controller). The control cvomputer 26 controls voltages suppliedto the beam deflector 15, the X-Y stage 46, the electron showergenerator 273, the ion shower generator 274, and the mesh electrode 275.Especially, the control computer (whole controller) 26 must effectcontrol so as to prevent electrons and ions blown by the electron showergenerator 273 and the ion shower generator 274 from affecting thesecondary electron signals detected by the secondary electron detector16.

The eleventh embodiment may also be applied to the above described firstto tenth embodiments. In the first to tenth embodiments, charges storedon the surface of the object 20 are counteracted by the electrons andions blown by the electron shower generator 273 and the ion showergenerator 274. In the detected images based upon secondary electrons orback-scattered electrons, therefore, contrast, for example, can be keptin a nearly constant state temporally.

The embodiments heretofore described bring about such an effect that itis possible to mitigate the charge-up phenomenon and charge-up easephenomenon caused when an object is exposed to an electron beam, setinspection conditions suitable for the surface section structure of theobject, and execute reliable inspection, measurement and image displayof the object.

The embodiments heretofore described bring about such an effect that itis possible to set inspection conditions suitable for the charge-upphenomenon and charge-up ease phenomenon caused when an object isexposed to an electron beam, and execute reliable inspection,measurement and image display of the object.

The embodiments heretofore described bring about such an effect thatsemiconductor substrates in the middle of fabrication can be actuallyinspected in the semiconductor fabrication line and consequently highlyreliable semicondutors can be obtained stably by using results of theinspection as control data for fabrication facilities forming thesemicondutor fabrication line.

What is claimed is:
 1. An electron beam inspection method comprising thestep of: irradiating an electron beam to an object to be inspected;detecting at least one of a secondary electron and a reflected electronemanated from the object by the irradiation of the electron beam;obtaining an image of the object from the detected electron; controllingan electric field in a neighborhood of the object for filtering anenergy of at least one of the secondary electron and the reflectedelectron emanated from the object so as to control the contrast of theimage; detecting at least one of the secondary electron and thereflected electron emanated from the object and passing through theelectric field in the neighborhood of the object by the irradiation ofthe electron beam; and conducting inspection or measurement of theobject on the basis of a detected signal of the detection in thecontrolled electric field.
 2. An electron beam inspection methodaccording to claim 1, wherein said electric field in the neighborhood ofthe object is 5 kV/mm or less.
 3. An electron beam inspection methodaccording to claim 1, further comprising the steps of displaying asignal representing the detected signal by the detection in thecontrolled electric field on a display means.
 4. An electron beaminspection method according to claim 1, further comprising the steps ofdetecting a height of the object, and controlling a focus of theelectron beam irradiating the object based on the detected height of theobject.
 5. An electron beam inspection method according to claim 1,wherein the step of controlling further includes at least one ofcontrolling an electric field on the object, a beam current, an imagedetection rate, image dimensions, pre charge of the surface of theobject and discharge of the surface of the object.
 6. An electron beaminspection apparatus comprising: an electron source; a beam deflectorfor deflecting an electron beam emitted from said electron source; aheight detector for detecting a height of a surface of an object to beinspected; an objective lens for focusing the electron beam emitted fromsaid electron source upon the object using an output from the heightdetector; potential control means for controlling an electric field in aneighborhood of the object; a sensor for detecting at least one of asecondary electron and reflected electron emanated from the object andpassing through the electric field in the neighborhood of the objectwhich is controlled by the potential control means by the irradiation ofthe electron beam; and image processing means for conducting inspectionor measurement of the object using an output from the sensor.
 7. Anelectron beam inspection method, comprising the steps of: irradiating anelectron beam to an object to be inspected; controlling an electricfield in a neighborhood of the object; filtering an energy of at leastone of a secondary electron and a reflected electron emanated from theobject in response to the irradiation of the object by the electronbeam; detecting at least one of the secondary electron and the reflectedelectron emanated from the object and having the energy thereoffiltered; obtaining an image of the object from the detected electron;and conducting inspection or measurement of the object using the imageobtained in the step of obtaining.
 8. An electron beam inspection methodaccording to claim 7, further comprising the steps of detecting a heightof the object, and controlling a focus of the electron beam irradiatingto the object based on the detected height of the object.
 9. An electronbeam inspection method, comprising the steps of: irradiating an electronbeam to an object to be inspected; controlling an electric field in aneighborhood of the object; deflecting at least one of a secondaryelectron and a reflected electron emanated from the object in responseto the irradiation of the object by the electron beam, the at least oneof the secondary electron and the reflected electron emanated from theobject having passed through an objective lens; detecting at least oneof the secondary electron and the reflected electron emanated from theobject and deflected after passing through the objective lens; obtainingan image of the object from the detected electron; and conductinginspection or measurement of the object using the image obtained in thestep of the obtaining.
 10. An electron beam inspection method accordingto claim 9, further comprising the steps of detecting a height of theobject, and controlling a focus of the electron beam irradiating theobject based on the detected height of the object.